magnetic pole, and is an electrical phenomena of the upper strata of the
atmosphere; and Chapter VII. is an attempt to explain the auroral light
as “probably produced by the collision of the subsidiary atoms when they
are in the act of electro-apposition.”
The pamphlet is said to be a condensed account of the discoveries of the
author in matters connected with atmospheric electricity—discoveries
which were described in papers handed to the Royal Society, but which
that Society did not read. The Royal Society were wise.
LE COUP DE FOUDRE DE L’ILE DU RHIN PRES DE STRASBOURG. PAR M. F.
HUGUENY. 4to. Paris. 1869.
(_Abstracted by G. J. Symons, F.R.S._)
A very full account of an accident by ball lightning. The facts are set
out as clearly as possible, the authority is given for every statement,
and most carefully engraved plans and engravings are given of all the
necessary details. It does not bear upon the question of lightning
conductors except in that it shows that a discharge of globular
lightning traversed a horizontal distance of 919 yards, passed in front,
but below the top, of a building which had three good conductors upon it
and struck a chestnut tree, which was by no means the highest tree in
the locality.
DIRECTIONS FOR CONSTRUCTING LIGHTNING RODS. _From_ “_Essays on
Meteorology_,” _by_ PROFESSOR JOSEPH HENRY.
(Smithsonian Miscellaneous Collections. 8vo., 1871.)
(_Abstracted by A. J. Frost_).
1. The rod should consist of round iron, of not less than ¾ of an inch
in diameter. A larger size is preferable to a smaller one (ordinary gas
pipe may be employed). Other forms of rod, such as flat or twisted, will
conduct the lightning, and in most cases answer sufficiently well. They
tend, however, to give off lateral sparks from the sharp edges at the
moment of the passage of the electricity through them, which might, in
some cases, set fire to very combustible materials.
2. It should be throughout its whole length in perfect metallic
continuity, either by screwing the parts firmly together or by welding.
3. The rod should be covered with a coating of black paint.
4. It should be terminated above with a single point, the cone of which
should be encased with platinum not less than 1/20 inch in thickness.
5. The shorter and more direct the rod is in its course to the earth the
better; acute angles should be avoided.
6. It should be fastened to the house by iron eyes, which may be
insulated by cylinders of glass; this, however, is not absolutely
necessary.
7. The connection to the earth should be as perfect as possible—in
cities nothing is better for this purpose than to unite it to the gas or
water pipes. When a connection cannot be formed in this way the rod
should terminate in a well containing water, or if this is not
practicable it should terminate in a plate of iron, or some other metal
buried in moist ground. It should, before it descends to the earth, be
bent, so as to pass off nearly at right angles to the side of the house,
and be buried in a trench, surrounded with powdered charcoal.
8. The rod should, in preference, be placed on the west side of the
house, and on chimnies where a current of heated air ascends during the
summer season.
9. A single rod may be placed on small houses, and its elevation should
be at least half of the distance to which its protection is expected to
extend.
10. Metallic roofs should be united with the lightning rods.
11. As a general rule, large masses of metal within the building,
particularly those which have perpendicular elevation, ought to be
connected with the rod.
ON LIGHTNING AND LIGHTNING CONDUCTORS. BY W. H. PREECE, Mem. Inst. C.E.
(Journal of the Society of Telegraph Engineers, 27 November, 1872.)
(_Abstracted by Prof. T. Hayter Lewis, F.S.A._)
The author refers to the Escurial having been on fire seven times—four
of them certainly from lightning; yet no lightning conductor is fixed
even now.
The average deaths from lightning in England are eighteen per annum; in
France, ninety-five.
From January 1, to July 31, 1872, 9·26 per cent. of instruments, of
different forms, used in the telegraph offices, were injured by
lightning.
Electricity is force, not matter, and _Current_ is a well-defined term
which implies a transference of electricity from one place to another.
Thunderstorms differ only in degree from the phenomena which cause the
ordinary snapping sparks from the machine.
In any case there must be two conducting masses in opposite electrical
states, separated by a non-conductor or dielectric.
The light is the effect of the discharge, and is simply incandescent
matter. It indicates the path of the discharge and nothing more.
Death by lightning is painless.
_Potential_ is that function of electricity which determines its motion
from one point to another.
The path of electrical discharge is prepared beforehand by induction.
The particles of air, &c., are in a state of “tottering equilibrium.” A
moving ship, a man on horseback may destroy this, and we have a
discharge with all the effects of light, heat, and mechanical energy.
It is very doubtful whether thunder-clouds are themselves the sources of
electricity, producing thunder and lightning; they are more probably,
mere accumulators as the coatings of a Leyden jar.
Clouds have been known to be absent during a discharge.
Moreover, the charge of a Leyden jar exists not in the coatings but in
the dielectric separating them.
So the discharge exists in the air and not in the clouds.
Sheet lightning is a mere reflection of forked.
Evidence proves that some such phenomena as ball or globular lightning
exists, and an explanation of it has been given by C. Varley.
Discharge is invariably through the line of least resistance. It may be
through metals, bricks, trees, animals, and not always in a single
track; it is often divided into two, three, or even four lines.
Thus, an electrical discharge in air, is simply a discharge between two
electrified conductors, of such different potentials as to break the
resistance of the dielectric separating them.
There is nothing hidden, mysterious, or unknown in it.
A ship is a prominent object; generally a conductor, and reduces the
line of resistance between the sea (inner coating) and the cloud
(exterior coating of the condenser) determining discharge.
Trees, buildings (except tall spires, &c.) are less prominent.
The effects of lightning experienced on telegraph wires, poles, and
instruments by direct discharge are less numerous than those by
induction, and seldom destructive.
There were only two cases in the past season where line wires (No. 8
iron, diameter 0·170 inch) were absolutely fused.
Accumulation of a charge upon a cloud converts it into a powerful
inducing body.
It induces in the wire an opposite electrical state. Discharge takes
place. The cloud suddenly loses its coercive power. The wire recovers
its neutral condition, and produces a powerful current in opposite
direction.
Wires are affected although buried two feet underground. Unprotected
poles are often destroyed. In one case, twenty successive poles were so.
Instruments have had their cases burst out, wood-work has been burnt,
and the wires of electro-magnets, &c., been fused.
Clouds are not perfect conductors, so do not part with all their
discharge at once. There may be several successive discharges.
_Protection._—Sir. W. S. Harris’s system approved.
_Houses._—Unnecessary expense is often incurred in protecting them.
A warm flue, terminating in a metal grate, is a dangerous conductor, as
it ends in the room and not in earth: hence so many accidents indoors. A
lightning conductor should expose a prominent metallic point, and offer
a path of little or no resistance thence to earth.
Hitherto expensive plates or ropes have been used for this. But the
author thinks galvanized iron wire ¼ inch diameter amply sufficient for
any dwelling house.
Telegraphic poles, protected by lightning conductors of No. 8 wire (½
the above size), have never been injured.
In one case, fifteen per cent. of unprotected poles have been struck.
But no case of damage has occurred for many years since the poles were
earth-wired. The cross-arms are often damaged as far as the earth wires,
never below.
The author can conceive no case in which ½ inch standard galvanized iron
wire is not ample.
The conductor should be solid and continuous from the gilded or platinum
point to the ground.
Joints should be well soldered. Chains and linked rods should not be
used.
Earth connections should be formed with iron gas- or water-mains, or be
several feet in coke, or in a well.
Each conductor should make a separate earth.
All masses of metal in the line of probable discharge are to be
connected with conductor.
Conductors should be examined periodically, they should not be
insulated, nor be near soft metal gas-pipes, nor bent in acute angles.
The area of protection appears to be that of a cone, whose radius is
equal to the height of the conductor.
One conductor is enough for small houses, but each stack of chimneys
should have one in connection with the main conductor.
Lead roofs and iron pipes are easily made into protectors for buildings.
Details given for protecting telegraph apparatus.
The telegraph companies abandoned the use of protectors. The Post Office
re-introduced them with good results. The Indian telegraph apparatus is
protected, and accidents scarcely ever occur.
_Prevention._—Points prevent the accumulation of charges. But with very
tall conductors—as to spires—a current results constantly in one
direction, producing electrolytic action and destruction of conductor,
as proved by one at Llandaff Cathedral.
So earth should be made with large masses of metal, as gas- or
water-mains.
Galvanised iron fastenings should not be used to secure copper
conductors to buildings, as galvanic action would be set up.
_Appendix._—Letters quoted from Mr. Latimer Clark and Dr. Faraday as to
damage to underground wires from lightning.
The _Discussion_ on Mr. Preece’s paper was conducted by Prof. Abel, Capt
D. Galton, Mr. G. J. Symons, who referred to Dr. Franklin’s suggestion
as to cold fusion, Prof. Ayrton, who entered at length into the system
of prevention used with the Indian telegraphs, Sir W. Thomson, and Mr.
Latimer Clark.
Mr. Preece replied, more especially alluding to the phenomena of fire
balls.
LIGHTNING RODS AND HOW TO CONSTRUCT THEM.——BY JOHN PHIN, C.E. New York.
1873.
(_Abstracted by W. H. Preece, C.E._)
The author is not an electrician nor a patentee, but the Editor of an
engineering paper called the _Technologist_. The book is written chiefly
to counteract the machinations of a great nuisance in the United States,
called the “lightning rod man.” The Author thinks a good rod as
important as a fire insurance policy. Every case of injury that he has
examined was due to defective rods, or to the absence of them. The
lightning rod is an American invention. He mentions several cases of
marked immunity from accident due to proper conductors, notably St.
Paul’s and the Monument, London; the Cathedral, Geneva; and St. Mark’s,
Venice.
The lightning rod should form the path of least resistance, and it may
be of iron or of copper. If of iron he prefers a flat bar 1 inch by ¼
inch, weighing 13 ounces per foot, or No. 00 copper, weighing 6½ ounces
per foot. He also advocates copper rope.
He thoroughly believes in the conduction through the mass of the metal,
and quotes (p. 12) several experiments in support of that view.
He believes in a good earth and in connecting all waterspouts, eaves,
gutters, and metal work generally with the earth and with the conductor;
he thinks one good rod enough, and sees no reason why lightning rods
should not be painted, indeed, thinks it better to do so, for they
become less unsightly; he has no faith in points, nor in gilding, or
platinising; he recommends instead cast iron caps to chimneys; he
discards insulation as absurd, and suggests that rods may be tacked, or
stapled, or strapped to buildings, although he prefers staples;
recommends strongly that wet earth should be reached, and that as large
a metal surface as possible should be exposed to the ground and embedded
in coke; he does not like any connections with the gas pipes.
He suggests that iron conductors may be welded or have merely butt
joints, but recommends solder with copper, after being bound with fine
wire.
He adduces the fact that Mr. Brooks, of Philadelphia, measured the
resistance of three rods attached to three buildings that had been
damaged, and found the average to be above the resistance of one hundred
miles of telegraph wire.
TRAITÉ DES PARATONNERES, &c. PAR A. CALLAUD. Paris. 1874. Royal 8vo.
(_Abstracted by Latimer Clark, C.E._)
This work consists of 171 pages. It commences with a short history of
the subject, which occupies the first chapter. The remaining nineteen
chapters treat successively of the collecting points and their mode of
action; the conducting rods and the methods of attachment to different
classes of building, and their connection with the earth, with
concluding observations.
The second chapter treats of the height of conductors and the area
protected, in which he follows the usual rules, and recommends lofty
rods, their office being not only to safeguard the building, but to
withdraw electricity silently from the air and thus prevent strokes of
lightning or diminish their violence.
In Chapter III., after citing the opinions of many other writers, he
strongly advocates protectors furnished with sharp points of platina, or
some inoxydisable metal, securely screwed and soldered on to copper
rods, and condemns points of iron or copper. Throughout the work he
treats cost as a secondary consideration and considers it false economy
to spare any expense necessary to ensure the thorough perfection of the
whole system.
In Chapters IV., V., and VI. he gives drawings of connections and of
various forms of weathercocks.
In Chapter VII. he recommends multiple points, especially in mountainous
countries and where storms are prevalent. He also points out that many
buildings are naturally protected by the metal roofs and ornaments
belonging to them. So long as these are connected with the ground, he
prefers that the projecting rod should be of round iron of considerable
length and in one piece, and the conducting cable should wind round it
as a collar, and be strongly attached to it by set screws and soldering.
He does not advise that all the masses of metal within a building should
be connected with a conductor, especially if they are in proximity with
human beings, but with a well-made conductor he considers it safer to
leave them isolated. (Chapter IX.)
For the conductor he recommends Gay Lussac’s construction, viz., a rod
of iron about ⅝ inch square, carried by iron supports, or a twisted
cable of iron wires having a diameter of ⅝ inch to ¾ inch, well tarred
or galvanised, 6 or 8 feet from the soil these are securely united to an
iron bar ⅝ inch to 1 inch diameter. If of copper they may be smaller.
Has seen rods of copper of ⅜ inch effectually protect churches, but
regards this as a minimum size for a length of 80 feet and ¾ inch as a
maximum. The single wires of the cords may have a diameter of 1
millimetre; the joints are made by splicing the strands together and
soldering them. (He recommends conductors of straw in some cases for
country use. Chapter X.)
The conductor is led along the ground in a channel of half drain tiles,
surrounded with coke and terminates in a copper grapnel embedded in a
basket of coke. (Chapter XIII.)
Chapters XIV., XV., and XVI. gives details of the construction of
lightning conductors for tall chimneys, powder magazines, and ships.
In Chapter XVIII. he gives numerous examples of the utility of
conductors, and in Chapter XIX. he gives a _resumé_ of his instructions,
again insisting on the perfect continuity of the connections and the
perfection of all the parts; these instructions are also embodied in a
note read before the Academie des Sciences, in 1862, a copy of which is
given at page 167 of M. Callaud’s work.
BLITZABLEITER-ANLAGEN. PROF. C. ZENGER’S SYMMETRISCHE BLITZABLEITER. C.
Korte and Co., Prague.
(_Abstracted by G. J. Symons, F.R.S._)
This is really a trade circular, but it gives, in a compact form, the
considerations which have induced Prof. Zenger to propose his new
system, and a description of the mode in which it is carried out. In the
first place it may be well to reprint from the _Meteorological
Magazine_, Vol. VIII. (1873), page 155, the report of the paper read by
Prof. Zenger at the British Association Meeting.
PROF. ZENGER, ON THE ACTION OF SYMMETRICAL CONDUCTORS AND LIGHTNING
CONDUCTORS.
Professor Zenger read a paper, on this subject, illustrating it with
the well-known experiment in physics of placing two insulated
hemispheres of brass plate in contact with another insulated sphere
of brass. If the former were charged with electricity and removed
from the inner brass sphere, there was found no trace of electricity
on its surface. The electricity was shown to be accumulated on the
surface of the outer spherical conductor, with equal tension in
every point of the surface. Professor Zenger showed that if the
outer hemispheres were replaced by two circular wires, no action
whatever in the inner conductor was found. He said it was easy to
see that this simple experiment might prove useful in regard to the
construction of electric apparatus and of lightning conductors to
protect buildings, and even whole cities, from the destructive
action of atmospheric lightning. He had, therefore, endeavoured to
ascertain the effects if any other form of a symmetrically-arranged
conductor were used, instead of a circular form. In the first
instance, he had tried the parabolic wires joined to the
electroscope; next, a rectangular wire with five different openings.
If placed exactly in the middle of the rectangular wire, no action
was observed; if placed eccentrically, however, there was small but
increasing action; and if he placed a needle or another
sharp-pointed instrument between the protecting wire and the
electroscope, he still better observed the different action produced
by placing the electroscope in an eccentrical position. He therefore
thought that it was possible by symmetrical wires placed on
buildings, or over whole cities, so to procure an entire protection
from atmospherical electricity. If the electric clouds should even
enter between the objects protected and the protecting wires, their
activity would be greatly diminished, for the wires would become
immediately charged, and nearly all the electricity accumulated on
their surface without any danger to the protected buildings.
Mr. Glaisher, who had taken the chair in the temporary absence of
the president, said their thanks were due to Professor Zenger for
his communication upon a subject so important. What they wanted to
know was the distance at which buildings were protected by a
lightning conductor, and Professor Zenger’s assertion that the
sections of a globe were as effective as the whole globe itself,
would be an important addition to scientific knowledge if proved to
be so.
Professor Clerk-Maxwell, who said he had paid some attention to the
subject of shielding bodies from electrical action by means of the
wire, feared that the form that Professor Zenger had given them
would be rather difficult to work out mathematically.
Professor Zenger said that the correspondent of the _Engineer_
newspaper had just informed him that the instrument hut of the
Atlantic Telegraph Company at Valencia was protected by wires on the
principle he had just mentioned, and the plan of protecting the hut
had been devised by Mr. Cromwell Varley.
We now pass on to Messrs. Korte’s paper, which refers entirely to the
application of this symmetrical principle to buildings. They begin by
claiming that Prof. Zenger’s system is the only one based upon
scientific investigations and practical experiments, and that although
far better than the primitive arrangements generally adopted it costs no
more. They urge that the conductors should be symmetrically arranged,
and yet they say that they should lead to the side of the house most
exposed to the weather. They recommend that the upper terminal should be
a long oval of gilt brass, something like a blunt spear-head, and that,
in ordinary cases, a single copper rod of 0·20 inch diameter (_not_ a
rope of that size) will be sufficient; it is to be taken through
porcelain insulators, and the earth terminal is to be a copper plate
nearly ¼ of an inch thick, buried from 6 to 9 feet deep in coke.
PROTECTION OF LIFE AND PROPERTY FROM LIGHTNING. By W. MCGREGOR. Bedford,
1875. 8vo. 43 pages.
(_Abstracted by Latimer Clark, C.E._)
Mr. McGregor does not give any new facts in connection with lightning,
but discusses the theory and action of conductors, and quotes numerous
opinions from other writers, with practical suggestions and precautions
to be observed in fixing conductors.
Among the principal opinions adduced are the following:—
1. Professor Jenkin’s statement, that if a conductor be armed with a
point, the electricity passes into the air rapidly in times of
excitement by induction, and so equalises the tension of the surrounding
atmosphere as to mitigate, or, in some cases, to prevent the discharge
of lightning.
2. De la Rive’s observation that a slight break of continuity in a
conductor is filled by a succession of brilliant sparks during a storm,
though there be no lightning; that blunt points or balls are equally
effective when struck, but are more usually accompanied by explosion
than by continuous discharge.
3. The opinions of De la Rive, Dr. Mann, and Preece, that a conductor
practically protects a conical space—of which the radius is about double
the height—and that the conductor should therefore extend to some height
above the building.
4. Ganot’s opinions that a conductor should terminate in a point or
points, have sufficient sectional area, be thoroughly connected with the
earth, and be connected with lateral metallic surfaces of large extent
if it passes near them; either iron or copper may be used, and existing
rain and water pipes, &c., may be utilised; but the joints should be
made carefully and tested. Chimneys with soot act as dangerous
conductors, and should therefore be protected.
The author does not give any precise directions as to the best form or
size of conductors.
LYNILDENS FARLIGHED I NORGE. BY H. MOHN, Kristiania. 1875.
(_Abstracted by C. Terkelsen._)
The author, having been specially commissioned to enquire into and
investigate the danger of lightning in Norway, found that lighthouses,
telegraph stations, and other much exposed buildings, which were
provided with conductors, did not by far suffer so much as churches,
which in the most cases were unprotected.
Out of about 100 churches reported to have been struck by lightning,
only three were provided with lightning conductors: on the first,
Kongsberg, the conductor was in good order, and the church was
comparatively uninjured; the second church, Fossnes, built of wood, had
a conductor, but made of zinc wire, which melted, and of course left the
church unprotected; on the third, Brónó (struck 17th October, 1872), the
wire had rusted, where it joins the earth, and the church was destroyed.
The author gives a full description of the different cases.
Of 100 churches struck by lightning, fifty-six were totally destroyed,
and had to be rebuilt; twenty-four of that number were churches built of
stone, twenty-nine of wood; the building material of the remaining three
is unknown. It would thus appear that stone buildings are almost as much
exposed to be damaged by lightning as wooden ones. Of the above-named
churches only one can be said to have been saved by a lightning
conductor, viz., Kongsberg. In 1820 the lightning struck the church, set
fire to a great part of the wood-work, and did other damage. The tower
was then covered with sheet iron. In 1852 the lightning struck the tower
again, which, however, then was provided with a conductor consisting of
two thin copper plates, 2½ inches wide, fastened on the north and south
side of the tower, and both beginning with the iron rod, on which the
vane is fastened; but this rod did not end in a point, but in a gilt
cross. The conductors were carried down the brickwork of the church to
the field, and across the market place, and ended in an old water-butt.
When the concussion took place one of the lightning conductors was
disabled; but no material injury was done to the tower. In 1872, July
16th, the lightning struck a farmhouse about 700 feet from the
above-mentioned church; the farmhouse being about thirty feet, and the
tower about 150 feet high.
The construction of a lightning conductor ought to be as follows: It
consists of the following three chief parts. (1) The receiver; (2) the
conductor; (3) the earth connection. The receiver consists of a copper
point 8 inches long and ¾ inch thick; which is screwed into an iron rod,
1½ to 2 inches thick. The screw must fit well and the flats of the
copper and iron fittings must be well connected and afterwards soldered
round the joint to prevent water and air from rusting the iron. There
are various ways of fastening the receiver to the building, but the
engineer is generally guided by circumstances. The conductor may be made
of iron or copper in the shape of rods or wire twisted like rope. If
made of iron rods they should be round and ⅝ to ¾ inch thick; if iron
wire-rope is used the thickness must be equal to a rod of ¾ inch; if
made of copper the rod must be at least ¼ inch thick, or if made of
copper wire-rope ⅜ inch. In both cases the conductor is put in metallic
connection with the receiver, and then guided into earth.
The earth connection is merely a continuation of the conductor and must
be buried as deep as possible in the earth, and reach the water, if it
is to be found.
The end which reaches the water may be constructed in various ways,
according to circumstances, but it is of the greatest importance that
the earth conductor never gets dry. If there is great difficulty in
getting at the water, the earth conductor may be constructed in the
following manner. It is made of copper, and has joined to it as many
branches as are thought necessary. Each branch has rivetted or soldered
to it a copper plate 1 or 2 feet square; they are carried as far away
from the building as possible, and buried deep into the earth. Besides
this there must be laid an extra conductor, perfectly metallically
connected with the chief conductor just under the surface of the earth,
alongside of it, out from the building, with as many branches, and as
long, as possible. This conductor becomes efficient, as soon as the
surface of the earth gets wet through rain, which generally falls during
a thunderstorm.
LECTURE DELIVERED BEFORE THE SOCIETY OF ARTS, _28th April, 1875_. By R.
J. MANN, M.D.
(_Abstracted by E. E. Dymond, F.M.S._)
Draws attention in the first place to certain established principles.
Different powers of various substances for conducting electricity.
Electrical induction.
In dull fine weather the surface of the earth negative, the surrounding
air commonly positive, the surface of the sea positive.
How a thunder storm begins, gradually approaching cloud, lightning
between it and earth. According to Delisle and Petit, a lightning stroke
_may_ extend 9 or 10 miles, but for ordinary circumstances the striking
distance varies between 650 and 6,500 feet. The lightning stroke follows
the line of least resistance, and invariably falls upon the most
prominent conducting substance, and passes through substances affording
an easy way and offering small resistance without disturbing their
molecular condition; shatters bad conductors; heats, sometimes melts,
good but insufficient ones.
Describes the various forms of lightning—flash, diffused, sheet, and
ball.
A continuous rod of good conducting metal must be carried from the top
of the building to the ground. Describes varying carrying capacities of
iron, zinc, or copper; recommends from his experience in South Africa,
42–strand rope of 1/16th inch galvanised iron wire.
The disintegrating energy is mainly expended on the extremities of the
conductor.
In Natal he used to enclose the top of the rope in a tube of stout zinc,
finished at the top by a gilded ball of wood, and he opened the strands
of the wire above it into a brush. The French electricians strongly
recommend a cluster of points.
The earth contact must be good and damp. The French system of Callaud
described.
Gay Lussac recommended that all large metallic masses should be brought
into connection with the conductor, and the conductor not insulated from
the building. M. Callaud, on the contrary, adopts insulating supports
for the conductor, and condemns the connecting of metals in the
building.
The metals used in the construction of the buildings may be utilised as
conductors; rain pipes, metal ventilating pipes, but not soft metal gas
pipes.
ON THE PROTECTION OF BUILDINGS FROM LIGHTNING. BY PROFESSOR J. CLERK
MAXWELL, F.R.S.
(Reprinted from the _Report of the British Association for the
Advancement of Science_, 1876.)
Most of those who have given directions for the construction of
lightning conductors have paid great attention to the upper and
lower extremities of the conductor. They recommend that the upper
extremity of the conductor should extend somewhat above the highest
part of the building to be protected, and that it should terminate
in a sharp point, and that the lower extremity should be carried as
far as possible into the conducting strata of the ground, so as to
“make” what telegraph engineers call “a good earth.”
The electrical effect of such an arrangement is to _tap_, as it
were, the gathering charge, by facilitating a quiet discharge
between the atmospheric accumulation and the earth. The erection of
the conductor will cause a somewhat greater number of discharges to
occur at the place than would have occurred if it had not been
erected, but each of these discharges will be smaller than those
which would have occurred without the conductor. It is probable,
also, that fewer discharges will occur in the region surrounding the
conductor. It appears to me that these arrangements are calculated
rather for the benefit of the surrounding country, and for the
relief of clouds labouring under an accumulation of electricity,
than for the protection of the building on which the conductor is
erected.
What we really wish is to prevent the possibility of an electric
discharge taking place within a certain region, say, the inside of a
gunpowder manufactory.
If this is clearly laid down as our object, the method of securing
it is equally clear.
An electric discharge cannot occur between two bodies unless the
difference of their potentials is sufficiently great compared with
the distance between them. If, therefore, we can keep the potentials
of all bodies within a certain region equal or nearly equal, no
discharge will take place between them. We may secure this by
connecting all these bodies by means of good conductors, such as
copper-wire ropes; but it is not necessary to do so; for it may be
shown by experiment that if every part of the surface surrounding a
certain region is at the same potential, every point within that
region must be at the same potential, provided no charged body is
placed within the region.
It would therefore be sufficient to surround our powder-mill with a
conducting material (to sheathe its roofs, walls, and ground-floor
with thick sheet-copper), and then no electrical effect could occur
within it on account of any thunderstorm outside.
There would be no need of any earth-connection. We might even place
a layer of asphalt between the copper floor and the ground, so as to
insulate the building. If the mill were then struck with lightning,
it would remain charged for some time, and a person standing on the
ground outside and touching the wall might receive a shock; but no
electrical effect would be perceived inside, even on the most
delicate electrometer. The potential of every thing inside, with
respect to the earth, would be suddenly raised or lowered, as the
case might be; but electric potential is not a physical condition,
but only a mathematical conception, so that no physical effect could
be perceived.
It is therefore not necessary to connect large masses of metal, such
as engines, tanks, &c., to the walls, if they are entirely within
the building.
If, however, any conductor, such as a telegraph wire or a metallic
supply-pipe for water or gas, comes into the building from without,
the potential of this conductor may be different from that of the
building, unless it is connected with the conducting shell of the
building. Hence the water or gas supply-pipes, if any enter the
building, must be connected to the system of lightning-conductors;
and since to connect a telegraph-wire with the conductor would
render the telegraph useless, no telegraph from without should be
allowed to enter a powder-mill, though there may be electric-bells
and other telegraph apparatus entirely within the building.
I have supposed the powder-mill to be entirely sheathed in thick
sheet-copper. This, however, is by no means necessary in order to
prevent any sensible electric effect taking place within it,
supposing it struck by lightning. It is quite sufficient to enclose
the building with a network of good conducting substance. For
instance, if a copper wire, say No. 4, B.W.G. (0·238 inch in
diameter), were carried round the foundation of a house, up each of
the corners and gables, and along the ridges, this would probably be
a sufficient protection for an ordinary building against any
thunderstorm in this climate. The copper wire may be built into the
wall to prevent theft, but it should be connected to any outside
metal, such as lead or zinc on the roof, and to metal rain-water
pipes.
In the case of a powder-mill, it might be advisable to make the
network closer by carrying one or two additional wires over the roof
and down the walls to the wire at the foundation. If there are
water- or gas-pipes which enter the building from without, these
must be connected with the system of conducting-wires; but if there
are no such metallic connections with distant points, it is not
necessary to take any pains to facilitate the escape of the
electricity into the earth.
It is desirable, however, to provide for the safety not only of the
building itself, but of the system of conductors which protects it.
The only parts of this system which are in any danger are the points
where the electricity enters and leaves it. If, therefore, the
system terminates above in a tall rod with a sharp point, and
downwards in an “earth wire,” the external discharge will be almost
certain to occur at the ends of these electrodes, and the only
possible damage will be the loss of a few particles from their
extremities; but even if the rod and wire were destroyed altogether,
the building would still be safe.
ON BOILER AND FACTORY CHIMNEYS AND LIGHTNING CONDUCTORS. BY R. WILSON.
1877.
(_Abstracted by Prof. T. Hayter Lewis, F.S.A._)
The author refers to the wide-spread disbelief in the efficiency of
conductors, the common opinion being that metallic bodies, especially
when pointed, attract lightning, and are therefore dangerous. This is
quite erroneous.
“On an electrified cloud passing over a pointed conductor, the opposite
and induced electricity of the earth is discharged from the point of the
conductor, and the cloud and air are often thereby neutralized without
producing lightning at all. But when a discharge does take place, the
conductor offers a line of comparatively small resistance.”
The author further says that, “if electrified clouds be driven to the
erection in such masses that the opposite electricity does not stream
away from the point of the conductor in sufficient quantities to prevent
a spark from passing, the spark or flash will pass from cloud to
conductor in preference to any neighbouring point.”
He refers to the safety of conductors, as shown by Sir W. S. Harris’s
reports.
When injury to buildings has occurred where lightning rods are fixed,
they have been “ignorantly and wrongly applied,” or joints have rusted,
the rods been broken, or earth contact has become imperfect.
He refers to Harris and Faraday as to sectional area of conductor.
Considers a rope to be better than a rod, as it is less liable to be
fractured and to have badly formed joints.
The upper extremity should project into the air as high as the diameter
of the chimney top.
The rod should not be inside a chimney, as gases are liable to injure
it.
The conductor should communicate with all metal in the chimney.
Insulation is not required.
All contact between copper and iron should be avoided on account of
galvanic action.
Earth contact should be tested every year. Anderson’s galvanometer
approved of for this.
NOUVEAU PARATONNERRE ACCEPTÉ PAR L’ACADÉMIE DES SCIENCES. PAR JARRIANT.
8vo. Paris. 1877.
(_Abstracted by G. J. Symons, F.R.S._)
This pamphlet is really a letter by M. Francisque Michel respecting some
new patterns of lightning conductors made by M. Jarriant, and submitted
to the Académie des Sciences by M. le Comte du Moncel. The author states
that there have been many theories as to the advantage of conductors
rising to great heights above buildings, and that, on the other hand,
some persons have urged that buildings should bristle all over with
points, and thus prevent any disruptive discharge. He thinks that, owing
to the translation of the storm-cloud by the wind, these short points
will not always have time to act, and says that the only rational plan
is to place a conductor high above the house it is intended to protect,
and so constructed that it, and it alone, offers a path of scarcely
appreciable resistance to the electric discharge. He says that in
Germany they put a metal sphere on the top of the conductors, but in
France, both the Academy and the Commission of the City of Paris have
advised that they should terminate in a point.
M. Francisque Michel says that formerly a conductor was supposed to
protect all objects within a cone whose base had a radius of twice the
height of the conductor; but that he and M. Félix Lucas had investigated
the question geometrically, and have arrived at the conclusion that the
radius cannot exceed 1·75 of the height. Hence, in many buildings, it
became necessary either to increase the number of the conductors or to
make them more lofty, both alternatives leading to increased expense. M.
Jarriant’s design, which consists of galvanized angle iron bolted
together, enables the increased elevation to be obtained at a price
twenty per cent. below that of the old patterns. The angle irons
themselves offer much surface, their angles are useful for discharging
electricity, and they carry at the top the copper terminal recommended
by the Académie.
A PRACTICAL TREATISE ON LIGHTNING CONDUCTORS. BY HENRY W. SPANG.
Philadelphia. 1877.
(_Abstracted by Prof. T. Hayter Lewis, F.S.A._)
“The identity of electricity, manifested by friction, with that
contained in the atmosphere, was not fully verified until Franklin’s
experiment with his kite in June, 1752.”
“In restoring the equilibrium between the opposite electricities of high
potential, the discharge will pass by the shortest path, even though a
poor conductor, in preference to a longer path through a good
conductor.”
The electricity of the earth is usually negative—of the atmosphere,
usually positive.
He quotes experiments at Kew to this effect.
The friction of solid and liquid particles against the earth, and
against each other in the air, produced by the wind, is a source of
atmospheric electricity.
The height of the lower part of the thunder-clouds above the sea in the
United States averages about 2,500 feet.
Dense thunder-clouds are good conductors, and are electrified to a
certain extent by the induction of the electricity contained in the
surface-earth. As electricity accumulates in the thunder-clouds it acts
by induction on the surface-earth, and causes a corresponding increase
of potential in the earth and the objects thereon.
He alludes to the vitreous tubes (fulgurites), 5 feet to 75 feet deep,
as being formed by electricity passing to the subterranean water-bed
through sand or other dry earth.
A highly positively electrified cloud within 3,000 feet of a building
causes the latter to be intensely negatively electrified by induction.
So also the earth beneath the building and the upper portion of the
subterranean water bed.
Whatever offers the _least_ resistance to the stroke will be its chosen
path and it will never leave a very good line of conductors, which is in
a short path between two opposite electricities, for an inferior one.
151 persons are killed by lightning annually in the United States,
France, England, and Switzerland.
He quotes Sir W. S. Harris’s system for the Navy as preventive.
There is no absolute safety anywhere out of doors. It can only be found
inside a structure having good conductors, with good earth connections.
Conductors cannot prevent disruptive discharge. They simply furnish a
good path for lightning which passes over them without doing any damage.
_Protective Area._—A committee appointed in 1875 by the Prefect of the
Seine reports as protected, a circular space whose radius is equal to
1·45 [Should be 1·75, see page (67). Ed.] of height of conductor. But
this is not always to be relied upon.
It is necessary that a conductor extend along the ridge, gable ends, and
eaves of a house, and above each chimney.
Lightning is electricity of very high potential, and the difference of
conductivity between the resistance of copper and iron to a lightning
discharge is small and practically amounts to nothing.
Iron rod conductors not to be less than 7/16 inch diameter. No case is
recorded where such a rod, properly connected with the earth, has been
fused or greatly heated by lightning.
Paint or an ordinary amount of rust does not affect conductivity.
A conductor of large surface exercises a much greater protective action
than the same quantity of metal in the form of a wire or solid rod.
Not because electricity in motion resides on the surface, but that the
expansive action of a discharge may have a wider scope _through_ the
metal.
So iron rain water-pipes are good conductors, and should be connected
with metal spouting, conductor on ridge, &c.
Cable conductors bend easily and can be made in one length, so often
answer better than bars.
If earth connection is good, rusty joints are of little consequence.
Conductors are not to be insulated.
Iron pipes for gas, water, heating, &c., also iron columns extending
from basement to near the roof are to be connected with conductor and
earth terminals.
The pipes on each side of gas meter are to be connected by iron bands.
Air terminals are to rise about 4 feet above each chimney or other
elevated projection.
High steeples to have horizontal conductors round them at every 20 feet
in height connected with vertical conductors.
One terminal in the centre of a building not over 25 feet long or wide
is sufficient, or one at each end of the ridge. One to each 20 feet of a
large building, with one at each end and to each chimney, &c.
When the horizontal portion of a lightning conductor, or path along the
roof of a building from ridge to eaves (_sic_) exceeds 50 feet in
length, the path becomes rather indirect for a lightning discharge,
which is then apt to select a shorter route through the building.
The upper part of terminal need not be gilt.
Points are practically of no use.
Chimneys are very likely to be struck, owing to the heated air rising
from them.
Provide against this by metal caps.
There is danger also, owing to the vapour rising from them, from barns
stored with new hay or grain, stables, schools, churches, &c.,
containing many people, flocks of sheep, &c.
Earth terminals must be in moist ground.
The author quotes Prof. F. Jenkin as to the difference of conductivity
between well moistened and perfectly dry earth (as porcelain, &c.) in
electricity of low potential, as 1,000,000,000,000 to 1.
Gas and water mains usually 4 feet or so deep in dry earth, therefore
not good conductors.
Examples quoted of injury to their joints by lightning, which passed
from conductors to the mains.
Suggests, as earth terminal, an iron pipe, 10 feet long, 2 inches
diameter, open at each end, perforated at sides, put in vertically, and
having the water from pipes for rain and waste led into it.
To be 8 feet from foundation.
Gives engravings of numerous forms proposed for conductors, most of them
being defective, and none show improvement on Franklin’s round rod.
Copper rods held by iron staples, and connected with iron earth
terminals, are bad, owing to galvanic action.
Copper wires in cable conductors become brittle, and snap when vibrated
by the wind; sometimes, also, they are eaten away by electrolytic
action.
He gives a drawing of a house protected as suggested by him, viz., by
metal rain water-pipes connected with the metal gutters and ridge; also
with his improved earth terminal by a good iron bar conductor.
Gas, water, and other pipes are to be connected together, and with
conductor.
These often give better path for lightning than the conductors.
But dangerous if without proper earth terminal.
He disagrees with Prof. C. Maxwell’s theory as to disconnecting the
metal covering, &c., of buildings from the earth.
Lightning conductors detached from buildings do not afford absolute
protection.
Lightning has great affinity for gas-holders, so one of the nearest
guide columns should be connected by a metallic conductor with the pipe
leading to street main, and also with a vertical earth terminal.
When a telegraph line is altogether metallic, well insulated upon poles,
&c., and not metallically connected with the earth, the electricity of a
storm-cloud will not exert so strong an inductive influence upon it as
upon a line whose ends terminate in the earth.
Line wire is often melted, poles and apparatus shattered, and employés
sometimes killed.
As a remedy, a galvanised iron wire is now fastened to every fourth pole
by iron staples, from 4 inches above the top of the pole to a coil about
10 feet long of iron wire beneath its lower end.
UEBER BLITZABLEITER UND BLITZSCHLÄGE IN GEBÄUDE WELCHE MIT
BLITZABLEITERN VERSEHEN WAREN. VON G. KARSTEN. Kiel. 8vo. 1877.
(_Abstracted by R. Van der Broek._)
In this pamphlet Dr. Karsten gives an account of two cases in which
buildings that were provided with lightning conductors were damaged by
lightning. The author states that the statistics for the year 1873 show
that in Schleswig-Holstein twenty-six per cent. of all the cases of fire
were caused by lightning; 1/130th part of these cases occurred in the
towns and the remainder in the country.
Do lightning conductors guarantee absolute protection? The author
answers this question as follows: There is no absolute certainty in
empirical matters; each new case may direct our attention to
circumstances that had been overlooked. If lightning conductors cannot
be said to ensure perfect safety, they certainly afford a very high
degree of protection.
The flash of lightning which struck the church at Garding, on the 18th
of May, 1877, fractured the conductor in fifteen places and pierced the
wall of the steeple in two places. The inefficiency of the conductor
resulted from the carelessness with which it was fixed; the line was
laid down the north side of the steeple and fastened with twenty-five
wall eyes; these wall eyes were hammered too deep into the wall, thus
damaging the line and forming a short and sharp bend in each case,
besides also unduly straining the wire. The damage to the steeple was
the consequence of a neglected secondary circuit. There are an
excessively large number of tie-rods in the steeple; the heads of these
rods are not connected together, neither are they, except in one case,
in close proximity to any of the larger masses of metal that are about
the building. The conductor passed close to one of those heads; the
south side of the steeple, where the opposite head is, becoming wet
through the rain, a secondary circuit was formed, and a return shock
followed; the damage to the steeple was trifling.
The rod was provided with a conical point rather blunt but surmounted by
a short platinum point. The copper line-wire was of good material—not of
a uniform thickness, but at the weakest places not weighing less than
240 grammes per lineal metre (8 oz. per yard or rather less than ¼ inch
diameter if solid). The earth-plate was sunk into a well 10 metres deep,
and tested faultless after the discharge.
ÉTUDE SUR LES PARATONNERRES LEUR CONSTRUCTION LEUR INSTALLATION. PAR
JARRIANT. 8vo. Paris. 1878.
(_Abstracted by G. J. Symons, F.R.S._)
This pamphlet opens with two pages devoted to the consideration of
Michaëlis’s work published in 1783, “De l’effet des pointes placées sur
le Templè de Salomon;” then it becomes more practical, refers to the
Academy of Bordeaux propounding in 1750 the question as to the identity
of lightning and electricity, and to Franklin’s letter in the same year
to Collinson, giving his reasons for believing in the analogy; states
that the experiments suggested by him were repeated by Buffon and
Dalibar in March, 1752, and subsequently repeated at Marly before Louis
XV. Then the writer refers to the erection of the first conductor in
France, to the popular displeasure which it excited, and to the long
legal process before the proprietor was allowed to keep it in position.
The author thinks that in many cases it is better to slightly increase
the number of conductors than to make them of excessive length, because
the latter course causes them to fatigue and jar the roof timbers by
their vibration with the wind.
Respecting platinum points he speaks strongly and to the following
effect:—“I have already mentioned that Franklin’s first conductor was
melted. Since then, the upper terminals of conductors have been made of
platinum, because it is the least fusible, the least oxidizable of all
metals, and a very suitable one for making into points. Moreover, the
sharper a point the greater its preventive action, and hence I condemn
every conductor without a platinum point. Although some manufacturers
employ simple copper cones, which may certainly last some time without
deterioration, believing in the desirability of the points being always
in perfect order, I reject their system entirely.”
Few persons are used to making platinum points, it is a Parisian
speciality, those which the author prefers, form a cone of about 10
degrees at the opening of the point and are about 1½ inches long, then
screwed and soldered into a mass of copper forming a nut on the conical
copper rod, which is 1 foot or 1 foot 6 inches long. The platinum point
thus mounted can only give rise to a galvanic action so extremely feeble
as not in the least to affect the durability of the apparatus. Some
persons for the sake of cheapness suppress this platinum point, but they
are wrong, the saving is slight and the result defective. The author
objects to conductors made of bar iron because the joints are always
defective, and if the section be too small they may be so heated as to
set fire to the charcoal in which the lower extremity is buried.(!)
However, the author prefers a rope, but he does not say whether of iron
or copper, and he puts a strand of hemp in the middle so as to make it
more pliable.
“Arrived at the ground the conductor ought not to be in immediate
contact with the earth, for the damp would slowly destroy it; we avoid
this (?) by making it pass through a trough filled with coke. Experience
has shown that iron thus buried in coke undergoes no change even during
thirty years.... Broken coke is better than charcoal because of the
great quantity of water which it absorbs.”
The author then says that after passing through this trough the
conductor must be continued into a well, or into very moist earth, and
should end with a discharger like a fork with many prongs.
He recommends that all the iron be galvanized.
Although the concluding paragraph, coming from a manufacturer, sounds
rather like self-recommendation, it undoubtedly contains important
truths. M. Jarriant says:—
“I cannot too strongly advise that in erecting conductors those
specialists should be employed, whose studies and constant practice
enable them to ensure perfect work. It is necessary also that every
workman should remember that in placing a lightning conductor he holds
in his hands the lives of men, that he should feel conscientiously
interested in the perfection of his work, and, finally, that he should
feel that it is a mission which he fulfils, and not a mere matter of
trade at which he works.”
REPORT ON THE LIGHTNING CONDUCTORS OF THE SMALL ARMS AMMUNITION FACTORY
AT DUM DUM, CALCUTTA. BY W. P. JOHNSTON. Government Telegraph Press.
1878. 4to.
(_Abstracted by W. H. Preece, C.E._)
This is an interesting report of a careful inspection and an electrical
testing, by a skilled electrician, of the lightning conductors at this
place. Although most carefully protected by well arranged and adequate
copper rods, copper bands, iron rods, and iron tubes, and terminated in
points, it was found that the points were covered either with rust or
with paint, and that the earth connections were so bad as to render the
buildings unsafe, although there was no difficulty in obtaining a good
earth at any part of the factory.
ATMOSPHERIC ELECTRICITY. BY DAVID BROOKS. Philadelphia. 1878. 8vo.
(_Abstracted by W. H. Preece, C.E._)
A pamphlet by a distinguished American telegraph engineer, giving his
view on the magnitude and origin of atmospheric electricity, which he
attributes principally to the friction of air on ice in the Polar
regions, and which circulates southwards in the higher regions of the
air, and northwards in the crust of the earth. Hence also Aurora
Borealis which is always preceded by high winds and most frequent when
the earth is covered with snow.
Thunderclouds are usually about 2 miles high and from 13 to 23 miles
thick. Lightning is much less frequent in mountainous than in plain
countries. Copper lightning conductors are often applied to iron ships
and iron buildings, but absurdly, as they are in such cases superfluous.
The author advocates immense earth plates where there are no gas- and
water-pipes, which he calls the best lightning rods ever erected,
because they are electrically in perfect connection with the earth. The
track of a railway makes a capital earth. He has never known an accident
where proper conductors were used, whereas he has known many accidents
from imperfectly and improperly constructed lightning rods, though of
the latest and most approved patents.
CATALOGUE MESSRS. A. COLLIN ET FILS, Article PARATONNERRES. Paris. 4to.
(_Abstracted by Prof. T. Hayter Lewis, F.S.A._)
The authors state that a Municipal Commission has recommended, to the
exclusion of all other points, copper about ¾ inch diameter, terminating
in a cone of 30°.
As to the area protected Messrs. Collin refer to the reports of the
Academy in 1823 and 1854, admitting, as a limit of protected area, a
circumference of which the radius equals double the height of the upper
terminal for slightly elevated buildings, and simply the height for
towers, &c., but this rule is badly defined.
The authors quote formulæ based upon the assumed altitude of the storm
cloud, but state them to be unreliable.
The Academy in 1854 reports that an electrified cloud is equally
attracted at equal distances by a metallic part of the roof and by the
terminal of the conductor.
Exposed points of pinnacles, &c., are to be united to main conductors.
If copper be too expensive use iron wire.
The conductors are to be supported at about 10 centimetres (4 ins.) from
walls and roofs.
The Academy recommends them to be isolated on glass or porcelain, but
the New Commission rejects this, and suggests that all metallic parts be
united to the conductor,—also recommends that wells be sunk to water
level, as earth connections.
But this would often entail a depth of 20 to 100 metres, or even more.
So the conductors may be sunk into moist earth and surrounded with coke,
and if necessary, may terminate in a sheet of copper.
A good earth is very important. Connection with water mains advised.
The authors have fixed 8,000 lightning conductors on their principle
without failure.
They give engravings of the various parts.
They engrave a diagram of a powder magazine which they propose to
protect by a tall isolated lightning conductor fixed at a distance from
it, and at such a height as that it will be included in a cone whose
radius is equal to the height of the conductor.
THE SCIENTIFIC AMERICAN, NOVEMBER 1st, 1879.
(_Abstracted by Alfred J. Frost._)
We learn that a lightning rod company in Cincinatti has patented a
system of lightning protection, which consists of an iron rod running
along the ridge of the building with points at each end projecting
upwards. It is supported upon large glass insulators, and has no
electrical connection with the building, and no rod running to the
ground. It is said that there are many public buildings in Iowa which
have been provided with this system of lightning rods.
Professor Macomber, of the Iowa Agricultural College, in reply to an
inquiry, says that it would be possible that a house insulated with a
glass foundation could be struck by lightning, but adds, “By insulating
a building the tendency to be struck by lightning would be very much
lessened, and the severity of the shock much decreased. Practical
illustrations of this can easily be obtained by means of an electrical
machine. A spark can be made to pass from the machine to an insulated
body, although the force of the shock will be much less than when not
insulated. Practically, it would be almost impossible to insulate a
building, because after rain commenced to fall it would wet it so that
communication with the earth would be established.”
REMARKS ON THE ATMOSPHERIC ELECTRICITY AND ON THE ACTION OF LIGHTNING
CONDUCTORS. BY PROF. DR. G. KARSTEN. 2nd edition. Kiel, 1879.
(_Abstracted by H. Van der Broek._)
The author of this pamphlet, Prof. Dr. G. Karsten, states that
thunderstorms are particularly dangerous in Schleswig-Holstein. He
attributes that fact to the scarcity of woods in that province, not more
than five per cent. of the surface being wooded; whilst in the Prussian
empire the proportion of woods is twenty-three per cent.
Woods promote a uniform dampness of the atmosphere and lessen the
up-current of air, which up-current contributes considerably to the
formation of thunderstorms; and the woods thus cause the discharges of
the electricity to take place principally between the clouds.
We do not yet know with certainty what the causes of atmospheric
electricity are, but we do know under what conditions or circumstances
thunderstorms may occur.
Thunderstorms are only formed when a violent condensation of the
rarified particles of water, which the atmosphere contains, takes place.
Such a sudden condensation, and the consequent formation of a
thunderstorm, may occur when two different masses of air—the one moist
and warm, the other dry and cold—intermix rapidly. The former of these
currents we call the South, or Equatorial current, the latter the North,
or Polar current. If these currents penetrate each other, or intermix
slowly, long continued falls of snow and rain ensue; if they mix rapidly
thunderstorms are formed during the warmer seasons, and sometimes also
during the colder seasons.
The Schleswig-Holstein Provincial Fire Insurance Association alone paid,
in sixteen years, the sum of £102,832 (an average of £6,427) for damages
caused by lightning. This province loses altogether £12,500 per annum
through fires caused by lightning.
The author’s very interesting remarks on the construction of lightning
conductors are briefly summarised in the following general rules:
1. Copper and iron form the best materials for lightning conductors;
lead and zinc may be used for secondary conductors.
(Nebenleitungen.)
2. If the conductor be constructed of iron, it should weigh from 1,200
to 3,400 grammes per metre (2½ lbs. to 7 lbs. per yard), according
to its length; a copper conductor should weigh, under the same
circumstances, from 250 to 600 grammes per metre (½ lb. to 1¼ lbs.
per yard).
3. The conductor must be connected with all the projecting corners and
pointed parts of the building.
4. There must be no sharp curves or bends in the conductor.
5. The conductor must be connected with all the large and extensive
masses of metal that may be about the building. This connection
may be made by wires leading towards the rod, as well as in the
direction of the earth contact.
6. The rods must be surmounted by good points, which must not be
liable to be fused by the discharges of the electricity.
7. The height of the rods must be in proportion to the size and shape
of the buildings; but it is better to erect several short rods
than one extraordinarily long one.
8. In making the connection with the earth all sharp curves must be
avoided.
9. The underground part of the conductor must be made of galvanized
metal, so as to minimise the effects of oxidation, or, in case a
layer of coke is used, to prevent the action of the sulphur.
10. The earth-contact should terminate in a plate, which, if possible,
should always be immersed in water. If this can be so arranged the
plate must have a surface ⅒th of a square metre (1 foot square)
for conductors for small buildings, whilst a plate of a surface of
2 square metres (5 feet square) will be sufficient for conductors
for the largest buildings.
11. Where a permanent contact with water cannot be established,
several plates of a larger size must be used, and laid in a
stratum of coke.
12. In the case of very large buildings, provided with several rods
and secondary conductors, several earth-contacts should be made
which should be connected with each other.
With reference to the upper terminal point, the author remarks, in an
appendix to the second edition of his pamphlet, that it should be made
of a conical form of a basis of from 20 to 30 millimetres (0·8 in. to
1·2 in.), and of a length of 150 millimetres (6 inches); it must consist
of pure copper and be gilded. It is useful to provide it with a platinum
needle 15 millimetres (half an inch) long, and about 4 millimetres (0·2
inch) thick at its base; or with a cone of chemically pure silver, the
proportion between whose base and height must be as 2 : 3.
LIGHTNING CONDUCTORS. BY RICHARD ANDERSON, London, 1879.
(_Abstracted by Prof. T. Hayter Lewis, F.S.A._)
_Historical Facts_—
The following are brief references to some of the principal facts
recorded in this volume:—
1600 A.D. Dr. Gilbert showed that magnetic and electrical phenomena were
emanations of one force.
1650. Otto Von Guericke constructed a little electrical machine (mainly
of a ball of sulphur on a revolving axis).
Sir I. Newton constructed a machine of glass, but used it merely for
amusement.
1675. The polarity of a ship’s compass was found to be reversed by a
stroke of lightning.
1708. Dr. Wall said that the light and crackling of rubbed amber seemed
in some degree to resemble lightning and thunder.
1709. F. Hauksbee, F.R.S., showed the similarity between the electric
flash and lightning.
1720. S. Gray, F.R.S., showed this by experiment, but was discredited.
1745. The first great step in this science was made at Leyden, by J. N.
Allamand and P. van Musschenbroek, who discovered the properties of the
Leyden jar. The priority of this invention disputed by Dr. Winckler, of
Leipzig; a mania for experiments arose. Louis XV. tried them,
unsuccessfully, on 180 of his Guards; but with perfect success on 700
Carthusian Monks.
1746. _Dr. Franklin_, of Philadelphia, saw some electrical experiments,
and in
1747 received a glass tube and some books on electricity from London;
then began to make experiments; sold his business, bought apparatus and
made electricity his study. Discovered that electricity passed most
easily and quickly through sharply pointed metals; that it was positive
and negative; and that lightning and electricity were identical. He sent
these results to the Royal Society, who refused to allow them to appear
in their Transactions; he then published them in a pamphlet. It was not
appreciated in England, but met with great applause in France, and was
also translated into German, Italian and Latin.
1747. The subject was taken up in England in a thoroughly practical
manner. Dr. Watson, Mr. Folkes, Lord C. Cavendish, Dr. Bevis, &c.,
experimented on a wire stretched across the Thames. The charge was found
to come back by the water. The same result followed through moist earth.
A gun was fired at a distance of four miles; the passage of the charge
appearing to be instantaneous.
New experiments were made by Dr. Watson with glass rods, 2 and 3 feet
long and 1 inch diameter. These showed that the rods, &c., contained
electricity only as a sponge holds water.
1752. Experiments by Messrs. Dalibard and De Lor, at Marly-la-Ville,
near Paris, in May, described.
1752. July. Franklin tried his Kite successfully, then his fame was
established, and he erected, on his own house, the first lightning rod.
1753. Prof. Richmann, St. Petersburg, was killed whilst experimenting.
The use of conductors opposed, violently in France, by Abbé Nollet.
1755. An earthquake at Massachusets, was laid to the charge of the
numerous lightning conductors. Franklin pushed their use by means of his
publication, “Poor Richard,” which had an enormous circulation;
particulars given showing success of lightning conductors.
1762. The first lightning conductor used in England, and Dr. Watson
asked to send in designs for lightning rods for ships. He did so, but in
an unpractical way, and they were disused.
1764. St. Bride’s steeple struck.
1769. The Dean and Chapter asked Royal Society for advice as to
protecting St. Paul’s. Committee of Royal Society disagreed as to
whether rods should be pointed. Pointed rods were used.
1769. The first conductor fixed to a public building in Europe was to a
church steeple in Hamburg.
De Saussure, at Geneva, had some difficulty in explaining to the
citizens that his conductors were not dangerous to his neighbours. There
was a great fear, generally, as to their use, _e.g._, a lightning rod
was erected, secretly, by the Priests at the Cathedral of Siena, and
excited great terror in the townsmen when discovered, but a terrific
stroke of lightning left the tower uninjured.
1772. Dr. Ingenhousz’s experiments.
1774. The University of Padua protected by conductors.
1777. A building at Purfleet was struck though it had a conductor, but
this was shown to be defective.
Sir J. Pringle had to resign his Presidency of the Royal Society because
he advocated points, but experiments were made and ended in favour of
points.
1778. The Venetians decreed that lightning rods should be erected
throughout the Republic.
1819. Electro-magnetism discovered by Œrsted.
1822. Sir W. S. Harris took up the question of providing good conductors
for ships, and afterwards made a list of 250 accidents to ships in 40
years; also of 200 seamen killed or wounded in that time. At this time
no importance was attached to the subject in England, except in the case
of Sir W. S. Harris. He insisted on the necessity of lightning rods. A
commission of inquiry was appointed by H.M. Government to investigate
the best method of applying lightning rods to H.M.’s ships, and they
reported (in 80 pages folio) that lightning rods were rather new fangled
things, but might be tried, without special harm to anybody. So most
ships were fitted with them after Sir W. S. Harris’s design. He was
knighted in 1847. An iron built ship, metal rigged, is as well protected
from lightning as Solomon’s Temple. Harris combated the opinion of those
who said that lightning rods attracted lightning.
Even in 1826 a government engineer recommended, on this ground, that all
lightning rods should be pulled down, and, in 1838, the Governor-General
of India ordered this by the advice of his “scientific officers.” This
was not countermanded until several buildings had been destroyed.
Army circulars are now regularly issued, containing Sir W. S. Harris’s
suggestions. (These quoted by Mr. Anderson).
Sir C. Barry suggested that Sir W. S. Harris should design lightning
conductors for new Houses of Parliament. He reported in 1855. He used
conductors of 2 inch copper tubes, ⅛th-inch thick, to towers and other
elevated parts, secured to masonry by metal staples. The cost was
£2,314.
As to conductors, Le Roy recommended that they should rise not less than
15 feet above chimney and summit of any edifice.
Mr. Anderson gives technical names of parts of lightning rods in
different countries. Chains first used, and gave rise to many accidents.
Tin and lead conductors tried; lead especially, from its easy
application to sharp curves, &c., but it is liable to be broken, and is
a bad conductor; so it went out of use.
Some particular buildings are constantly under attack from lightning,
_e.g._, Church of Rosenberg in Carinthia, not standing in a very high
position, but greviously damaged in 1730, &c.; rebuilt in 1778, with
lightning rod, and not injured since. Some of these effects may be
explained on meteorological grounds: the height and thickness of the
charged clouds only slightly varying, perhaps, in districts where there
are prevailing winds. The height of clouds sometimes enormous. Instances
are given of their being 15,000 to 25,000 feet above the sea. But
sometimes clouds are almost flat on the earth, two instances are given
of this. A remarkable and often fatal discharge is the “return stroke,”
always less violent than the direct stroke, but often very powerful, and
caused by the inductive action exerted by a thunder-cloud. Men and
animals are charged with opposite electricity to the cloud. When the
latter is discharged by the recombination of its electricity with that
of the ground, the induction ceases, and all bodies charged by induction
return to a neutral condition. Hence the dangerous “return stroke.” Lord
Mahon first demonstrated this by experiment. _As to origin_ of
atmospheric electricity, De Saussure considered it due to the
evaporation of water by the sun’s heat. Peltier (1765–1845) considered
the earth itself to be one immense reservoir of electricity. As light
comes from the sun, so electricity is generated by heat from the
interior of the globe. No electricity is produced by atmosphere, nor
held by it, except temporarily.
There is no recorded case in which a well made lightning rod, with “good
earth,” did not do its duty.
In 1822 there was an extraordinary number of thunder storms in France,
so lightning rods were ordered by Minister of Interior for all public
buildings, and he applied to the Academy of Sciences for advice. 1823. A
Committee (Gray Lussac, &c.) reported. They laid it down, as a rule,
that a lightning rod protected a circular area, having a radius of
double the height of the rod; and they said nothing about regular
inspection of lightning rods. So disasters occurred, and another
Committee was appointed (Pouillet, &c.). They reported 1854. The theory
as to the protected area was abandoned. It was recommended that
lightning rods should have as few joints as possible. The joints to be
well soldered, the points to be of copper (not platinum), and not to be
very finely pointed. The rods to be of copper, not iron. The Louvre was
well protected by lightning rods, but slightly injured, 1854. Another
Committee was appointed, and, 1855, Pouillet again reported on its
behalf. It recommended that the points (always of copper) should be
thicker, and the rod to have a never-failing connection with water or
moist earth, 1866. Several French powder magazines were struck though
provided with lightning rods, and the Minister of War asked the Academy
for another report. Another Committee (Becquerel, &c.) was appointed,
and, 1867, Pouillet again reported. He defines lightning as an immense
electric spark passing from one cloud to another, or from cloud to
earth, to restore equilibrium. The best protection for a building would
be iron rods surrounding it on all sides, and passing deep into ground.
Conductors should be inspected every year.
The conductor now remains essentially as Franklin invented it. Of the
inner nature of “lightning” we are utterly ignorant. The first
conductors were always of iron as being cheap.
Sir H. Davy pointed out the different conducting powers of different
metals. Becquerel, Lenz, Ohm, and Pouillet made similar investigations,
with the following results:—
───────────┬─────────┬─────────┬─────────┬─────────┬─────────┬─────────
│ Silver. │ Copper. │ Lead. │ Tin. │ Iron. │Iron = 1
│ │ │ │ │ │Copper =
───────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────
│ │ │ │ │ │
Davy │ 109·1 │ 100 │ 69·1 │ │ 14·6 │ 6·85
│ │ │ │ │ │
Becquerel │ 73·5 │ 100 │ 8·3 │ 15·5 │ 15·8 │ 6·33
│ │ │ │ │ │
Lenz │ 136·25 │ 100 │ 14·62 │ 30·84 │ 17·74 │ 5·64
│ │ │ │ │ │
Ohm │ 35·60 │ 100 │ 9·7 │ 16·8 │ 17·4 │ 5·75
│ │ │ │ │ │
Pouillet │ 81·26 │ 100 │ │ │ 18·2 to │ 5·49 to
│ │ │ │ │ 15·6 │ 6·41
───────────┴─────────┴─────────┴─────────┴─────────┴─────────┴─────────
(The difference being owing, probably, to the greater or less purity of
the Metals.)
1815. Brass wire rope generally used in Bavaria, but a steeple was
struck down though with a brass wire conductor 1 inch diameter. The real
defect was “bad earth,” but attributed to bad form of conductor; so this
was abandoned. Brass not a reliable metal, and often destroyed by smoke.
Purity of copper essential.
Professor Matthiessens’ experiments shewed that the conductivity of
copper varied from—
Pure 100·
to Australian 88·86
Russian 59·34
and Spanish, Rio Tinto 14·24
Hotel de Ville, Brussels, lightning rods designed by Professor Melsens
on the principle of a great number of small ones in preference to one of
large size, and covering building with network of metal, having many
points and many earth contacts. He considers that the relation of
section to surface of the lightning rod has a marked and definite,
though unknown, result.
Author describes weathercocks and methods of fixing them.
_Lightning rods generally_—methods used in France: Terminal rods,
usually of wrought iron, galvanized; their height depends on the size
and area of building it protects. This is generally to be considered to
be within a cone of revolution, of which the radius = height of rod
above ridge × 1·75.
Points described. The conductors are of iron, rebated, soldered, and
bolted at joints, with lead between. Bent plates of copper introduced to
provide against contraction and expansion. In large buildings, metallic
connections are formed on ridge by iron bars-¾ in. × ¾ in.
Precautions are taken against the destruction of iron underground, viz.,
by enclosing it in vertical sprints of wood, tarred or creosoted, rising
a few inches above ground, or by a coating of tar or by a wrapper of
sheet lead. The earth connection is a trough filled with broken
charcoal, through which the conductor passes, ending in several
branches, or in a grating between layers of charcoal. Galvanized iron
cables sometimes used, and (rarely) copper of ½ in. diameter.
_America._ Gutters and water pipes, &c., used where possible. If the
roof be of wood, slate, &c., a conductor is laid along ridge, and
connected with gutters and rain water pipes. If these latter be less
than 3 in. diameter, the conductor is often extended from roof down the
side of building close to the pipe. All metal chimney caps, railings,
water and gas pipes, and other large or long pieces of metal, inside and
out, are connected with conductor. The upper terminal usually projects 4
ft. above chimney or other highest part of building. It is a round rod,
7/16th in. diameter, hammered out to join it to conductor. A building 25
ft. wide and broad has one terminal in centre and one at each end. In
larger buildings, one terminal to each 20 ft. of roof. Not always
pointed.
Steeples have horizontal conductors at every 20 feet, connected with
vertical conductors, to provide against discharge in centre, caused by
deflection of discharge in the air by rain. Conductors are fixed to
buildings by iron staples or straps; the earth connections are similar
to ours. Also are used iron pipes, about 3 in. diameter and 10 ft. long,
placed vertically in moist earth and carefully connected with conductor.
_Newall’s system_: Copper conductors are the best, and in the end,
cheapest. Terminal rods are usually 3 to 5 ft. long, and ⅝th to ¾ in.
diameter, branching out at top.
_German_ “reception rod” described as being of iron, 10 to 30 ft. long;
the area of protection theory discredited. The electric fire, seeking
its nearest path to earth, is not to be diverged from it to the rod.
These high rods of no use except, _e.g._, near high trees, and are often
dangerous from being blown down. Barns containing new hay are likely to
be struck, as hay sends out stream of warm air.
Designs explained for protecting private houses by short terminal points
to chimneys, gables, &c. A copper rope at least ⅝th in. diameter should
be used; a copper rod, ½ in. diameter, has never been fused, so far as
is known. In chimneys of manufactories, where rope is liable to
corrosion, a greater thickness should be used.
Laughton-en-le-Morthen steeple injured, though with lightning rod, but
this was only a small, thin copper tube, ⅞th in. external diameter, and
1/32 in. thick; weighing 8oz. per foot, or equal to a rod about 0·12 in.
diameter, the joints were corroded, and the earth contact was imperfect.
Nevertheless, only one buttress was injured. It is of little consequence
whether the conductor be inside or outside, if it be carried to earth by
the shortest route. At first it was more generally put inside in France,
but this was given up for fear of accidents. But it is beyond
controversy that a good conductor is absolutely harmless to all
surrounding objects, and a man might lean against a copper half-inch
rod, carrying off a heavy stroke of lightning into “good earth,” without
being aware of its passing.
It is useless and dangerous to isolate conductors from buildings. All
masses of metal should be connected with conductors.
Prof. Clerk Maxwell’s theory described (as to disconnecting the
conductors, &c., from the earth): He states that it is not necessary to
connect masses of metal, as engine tanks, &c., if entirely within the
building, unless a conductor as, _e.g._, telegraph wire, water or gas
pipe come into the building from outside, then they must be connected
with conductor.
List of accidents from lightning, also deaths or injuries in England and
Wales, Prussia, United States, Sweden and Austria.
Particulars of damage to St. George’s Church, Leicester, 1846, and to
West-end Church, Southampton. Also, to Merton College, Oxford, and St.
Bride’s Church, Fleet Street, none of these having lightning rods.
Wrexham Church struck, this had a copper conductor, but it was too small
and the earth contact was doubtful.
List of buildings struck at home and abroad from 1589 to September,
1879, the authorities for the statements being given.
List of powder magazines struck between 1732 and 1878.
_Earth Connections._ Franklin’s report, 1772, strongly urges the
importance of this, in speaking of the powder magazine at Purfleet. In
ordinary cases, moist earth is sufficient, but in such a case as this he
recommends that a well should be dug at each end of magazine, with 3 to
4 ft. of water in it.
The importance of “good earth” is shewn by numerous accidents to
buildings, as, _e.g._, in 1779, the church of St. Mary, Genoa, and, in
1872, the cathedral of Alatri, in which latter case, the discharge left
moist earth to pass off by a water pipe, which it broke; but the church
was uninjured. Also at Clevedon Church, where the conductor passed into
a drain which was dry, but the stroke merely injured one buttress and
passed off by gas and water pipes.
Mr. Anderson states that earth contacts must be large. That it is
important that metal work be connected with lightning rod in at least
two parts, to realize a closed metallic circuit, and so offer entry and
exit. The earth contacts of the eight conductors of the Hotel de Ville,
Brussels, described, viz., their being enclosed in an iron box, 8 in. ×
3 in. × 3½ in., with three series of conductors (details given): one
passing into a well, another to the gas main, the third to water main.
In ordinary buildings, the grating, with charcoal, coke, or cinders,
&c., as before described, may be sufficient; but with large buildings,
contact with water is absolutely necessary.
_Periodical inspection._ Author strongly urges this because conductors
deteriorate from action of wind and weather above ground; the “earth”
often becomes bad, owing to new drains, &c.; buildings may be altered in
regard of the quantity and position of metals. An instance is given of
damage to a building owing to the change of position of iron safe.
Conductors are often displaced by workmen; and the number and position
of new gas and water mains, new trees, &c., also influence the power of
conductors.
_Appendix._ This contains a very full list of books relating to
lightning conductors.
REPORT UPON LIGHTNING DISCHARGES IN THE PROVINCE OF SCHLESWIG-HOLSTEIN.
BY DR. LEONHARD WEBER. 1880. 8vo.
(_Abstracted by Alexander Siemens_).
The serious damage caused in Schleswig-Holstein by lightning led to an
official inquiry into the subject, the following is an abstract of the
first report of the commission.
It is stated that trees, by their gradual but uninterrupted discharge of
electricity, have a dispersing effect upon thunder-clouds, and tend to
lessen the energy of lightning. In six cases out of the twelve examined,
houses with trees close by, were struck, but not so heavily as in
another case where the building had no protection whatever. Trees do
not, however, afford complete protection to neighbouring buildings,
their conductive capacities not being sufficient to convey, in the
immeasurably short time required, such heavy discharges of electricity
as lightning flashes. This is instanced by their being often wholly, or
partially, destroyed by the current, or, as occurred in four cases, by
their passing it over to better conductors, buildings, &c.
If a thunder-cloud passed over a perfectly plane surface, the discharge
would take place in a vertical line between earth and cloud, but
prominent objects, such as isolated trees, buildings, lightning
conductors, and iron pumps, reaching down to underground water, act as
attractive points, and divert the discharge, the path of which is also
influenced by any conductors which happen to come between them and the
thunder-cloud, such influence depending upon the capacity of the
conductors. So that, generally an electric discharge chooses that path
which, taking the distance into account, offers the best means of
conduction.
It is frequently found that inflammable material is struck by lightning
without being ignited, on account, it is presumed, of the short duration
of discharge not allowing the material to become sufficiently hot to
burn, but whether the duration of discharge is dependent upon the nature
of the charge of the thunder-cloud, or solely upon the condition of the
objects struck, has not been ascertained. The latter is, however, not
without influence, as in two of the four cases which resulted in fire,
the cause was presumably due to newly gathered hay stored at the top of
the houses struck, and in the other two cases to trees, which were
struck at the same time, the hay and the trees being bad conductors, and
prolonging the duration of discharge.
Four cases are given of buildings having lightning conductors being
struck.
The first case is that of a windmill, the conductor of which terminated
in a sheet of metal placed in a well near the building. The discharge
was exceedingly heavy, but beyond the platinum point being almost
entirely fused, no other damage was done.
The second is that of a house with two separate lightning conductors,
each ending in a copper plate, spirally coiled up, and laid in
underground water. One of the conductors was struck, and the lightning
passed from it, and, running horizontally along the thatched roof of the
house, descended by the other, causing no damage.
The third case refers to a church and, adjoining it, a school building.
A portion of the discharge was diverted from the conductor by an anchor
in the church wall three metres off (which it magnetized), and forced
its way through the ceiling of the school-house to a number of gas
brackets, which were turned up towards the ceiling. It was ascertained
that the ground floor of the house was completely under water, and well
connected to earth through the gas mains and an iron pump, a good
continuous conductor thus being formed.
Accordingly, the report recommends that lightning conductors should be
connected to the large masses of metal, such as gas and water mains,
which are found in our houses.
In the fourth instance a church had a lightning conductor, which was
connected to the top of two large iron supports running through the
steeple to the nave, and which terminated in a coiled earth-plate, 1 sq.
metre (11 sq. ft.), supposed to lie in water 7 metres (23 ft.)
underground. The lightning struck the conductor and, passing to the iron
supports, sprang from one through the outer wall, close to an iron
window frame, and from the other across the stucco ceiling, going to
earth 100 feet off through the altar gilding, which it blackened. It was
subsequently found that the copper earth-plate was only ⅓ metre (1 ft. 1
in. sq.), and that it was buried loosely round the rod in dry sand, the
rod itself reaching 2 to 3 metres further down, and just touching water
without an earth-plate, and also that the two supports had no earth
connection, thus forming a great danger instead of a safeguard to the
church.
DIE KONSTRUKTION UND ANLEGUNG DER BLITZABLEITER ZUM SCHUTZE ALLER ARTEN
VON GEBÄUDEN SEESCHIFFEN UND TELEGRAFEN STATIONEN. VON DR. OTTO BUCHNER.
Weimar. 1867. 8vo.
(_Abstracted by R. Van der Broek._)
The book is divided into two parts:
1. General, or Introductory, and
2. Practical.
The first, or Introductory part, is sub-divided into:
1. Historical and statistical notes;
2. The theory of atmospheric electricity, and of the lightning
conductor; and
3. A chapter on natural lightning conductors.
The great philosopher, Lichtenberg, of Gottingen, said in the year 1794:
“People are struck and their dwellings are destroyed by lightning
because they will have it so. It does not matter to us whether
parsimony, carelessness, ignorance, or anything else is the cause of
this.” The author asserts that this dictum may be equally applied to the
present generation.
Professor J. H. Winkler, of Leipzig, discovered, in the year 1746, that
electricity is the principal cause of thunderstorms.
The first lightning conductor in Germany was erected 1769, at Hamburg,
on the steeple of the Jacobi Church.
Between the years 1835 and 1863, a period of 19 years, 2238 persons were
_killed_ by lightning in France. The maximum in one year (1835) was 111
and the minimum 48. The total number of persons _struck_ by lightning
amounted to 6714; of this large number 1700 persons would have escaped,
if they had been careful to avoid the neighbourhood of trees, whilst the
storms were raging. The greatest number of the accidents caused by
lightning occur during the months of July and August; not a single fatal
case is on record for the months of November, December, January, and
February. The annual average number of persons killed by lightning was 3
in Belgium, 22 in England, and 10 in Sweden. In the low-lying
Departments of France the average is 2 or 3; the average increases
rapidly for the Mountainous Departments to 24, 28, 38, 44, and (in
Auvergne) 48. The per centage of males in France is 67, females 10, and
in the remaining cases the sex was not stated. In Prussia the proportion
is 184 males to 105 females, in Sweden 5 males to 3 females.
The largest number of persons killed by _one_ discharge is 8 or 9.
The author states that the return shock is only mechanical in its
effects.
Professor Müller lays down the following conditions for lightning
conductors:—
1. The rod must end in a very sharp point.
2. There must be no want of continuity between the extreme point and the
earth contact: and
3. The different parts of the conductor must be of the requisite
dimensions.
In practice we find that the first mentioned condition is incorrect, as
sharp points are too liable to be fused.
The rod must be made of a pyramidal or a conical form. Short rods of not
above 2 metres (6 feet 7 inches) in length may be made of a cylindrical
form. The best form of rod is one tapering from a base of from 50 to 60
millimetres (2 inches to 2·4 inches) in diameter to a diameter of not
less than 14 millimetres (0·56 inches). As it is difficult to fix rods
of a height of 10 metres (33 feet), it is better to erect one long rod,
and several shorter ones on different parts of the roof and connect them
together. The principal rod should have a height of from 2½ to 3 metres
(8 to 10 feet) and the secondary rods (_Nebenstangen_) should be at
least 1 metre (3 feet 3 inches) high.
The form of point universally used in Germany is a strongly firegilded
copper cone.
Kuhn advocates the use of chemically pure silver for the points. His
arguments in favour of this metal are incontrovertible. The conducting
power of silver is 1·36; that of pure copper being 1. The fusibility of
silver (1,000 c.) is sufficiently high for the purpose. The atmosphere,
unless it contains sulphur in a gaseous or a liquid form, has no effect
on silver. Silver is cheaper than platinum, and not more expensive than
a gilded copper cone, and it can be easily soldered to other metals.
The point should be screwed on, as well as soldered to the rod. All
other but the conical form of point should be rejected.
The best material for the earth contact is galvanised iron.
As regards the protection of sea-going vessels, Snow Harris’s
arrangement, converting, as it were, the vessel into one mass of metal,
is perfect.
The first practicable lightning conductor for the protection of
telegraph wires was constructed by Steinheil in 1846. His arrangement
was somewhat modified by Breguet and Fardely. Meiszner introduced a real
improvement.
On the Prussian railway telegraphs two “point-systems” are in use, one
for small stations, and the other for larger stations.
It is desirable that all lightning conductors be examined once a year.
The metallic connection throughout must be perfect, the point must be
kept free from rust, and the earth contact must be good. The whole
circuit should also be tested by means of a battery and a galvanometer.
EARTH CONNECTIONS OF LIGHTNING CONDUCTORS. BY LIEUT.-COL. STOTHERD, R.E.
(Journal of the Society of Telegraph Engineers, May 12, 1875.)
(_Abstracted by W. H. Preece, C.E._)
Arguing from the case of a powder magazine at East London, Cape of Good
Hope, when the iron conductor was led into a cemented water-tank,
frequently dry, and where it was destroyed, the author raises two
questions:
1. Should such tanks be used for earth?
2. Is iron the proper metal to use?
He gives a decided negative reply to the first, and advocates the use of
galvanized iron properly protected from atmospheric action. He suggests
rods 1 inch in diameter, or bands 2in. × ⅜in. thick.
In the discussion which followed it was mentioned that the ground about
Torquay is so insulated that plates had to be carried out to sea to
secure a good earth for the telegraph there, and that of the numerous
churches which had been inspected, there was not a single conductor that
could be passed. It was pointed out that when copper conductors were
fixed with iron wall-eyes—a frequent thing—galvanic currents were set
up, and the conductor destroyed at the ground line.
It was stated that the earth connection of a supposed perfect conductor
was found to be equal to a resistance of 1,000 Ohms.
Mr. Preece, Major Malcolm, R.E., Dr. Mann, Mr. Pidgeon, Mr. Kempe, Mr.
Graves, Mr. Spagnoletti, and Mr. Latimer Clark, took part in the
discussion.
REMARKS ON SOME PRACTICAL POINTS CONNECTED WITH THE CONSTRUCTION OF
LIGHTNING CONDUCTORS. By R. J. MANN, M.D., F.R.A.S. (_Quarterly Journal
Meteor. Soc._, October, 1875).
(_Abstracted by G. J. Symons, F.R.S._)
States that there are certain principles accepted as established facts,
_e.g._, that conductors should be of metal of high conductivity, and of
adequate dimensions. That in 1854 the French electricians held that a
“quadrangular iron bar ¾ in. diameter, was sufficient in conducting
power for all purposes.” Since then, wire ropes, owing to their
pliability, have nearly superseded solid rods, and copper has been
preferred to iron because of its higher conducting power and less
liability to oxidise. But provided that the iron be galvanized, and of
five times the sectional area of a copper conductor, considers the metal
immaterial.
Author states that the resistance of a conductor increases with its
length, therefore sectional area of conductor must be increased for
lofty buildings. Modern French electricians employ copper rope 0·4 to
0·8 in. diameter. M. R. Francisque Michel considers galvanized iron wire
rope 0·8 in. diameter sufficient for all ordinary cases. Copper wire
rope 0·5 in. diameter (6¾ oz. per foot) recently applied to St. Paul’s
Cathedral.
Importance of perfect earth connection strongly insisted upon, but it is
matter of some difficulty, and the oxidation of the earth terminals, and
their inefficiency doubtless lead to most of the reported failures of
lightning conductors. Author quotes Pouillet and Becquerel, as saying,
that for the efficient discharge of the lightning, which could be
carried by a copper rod 0·8 in. diameter, contact must be obtained with
1,200 square yards of moist earth, but this large requirement can only
easily be obtained in towns by connection with the water mains. Various
modes of obtaining adequate earth contact by iron harrows, Callaud’s
grapnel in basket of coke, &c., described.
Explains the rationale of testing goodness of earth currents by the
galvanometer. Calls attention to the destruction of upper terminals of
conductors to factory chimneys by the emission of sulphurous fumes, and
suggests that they might be cased in lead.
Calls attention to the importance of every joint being made absolutely
perfect.
Urges the superiority of points for upper terminals, owing to their
facilitating silent discharge, and rendering lateral discharges from the
conductor less probable.
Thinks that multiple points of copper kept fairly sharp and clean are,
on the whole, the best upper terminals.
Considers that all large masses of metal in a building should be
connected with the conductor; but quotes M. Callaud, who holds the
opposite view. Dr. Mann, however, points out that if the conductor be
efficient and perfect, the accidents which M. Callaud contemplates, and
on which he bases his arguments, could not occur.
Calls attention to the ready path afforded by the column of heated smoke
discharged by chimneys, and hence alludes to the placing of a coronal
conductor, as well as a multiple point on important chimneys.
Suggests the utilization of rain water pipes, by perfecting their
joints, and securing a good earth connection at their base.
ON THE PROTECTION OF BUILDINGS FROM LIGHTNING. By R. S. BROUGH, 4to,
MUSSOORIE, 1878.
(_Abstracted by W. H. Preece, C.E._)
A carefully prepared theoretical and practical paper, adapted for use in
India. Author advocates the use of iron from its higher temperature of
fusion, and greater specific heat than copper, its long protection from
decay by galvanization and its cheapness. He prefers wire cables from
the absence of joints in them. He gives precise instructions for the
formation of a good earth, and advocates periodic electrical tests.
LIGHTNING CONDUCTORS. By Professors AYRTON and PERRY. (_Journal Society
of Telegraph Engineers._ Vol. V., 1876, p. 412.)
(_Abstracted by W. H. Preece, C.E._)
The authors controvert Clark Maxwell’s views that a building would be
perfectly protected from lightning by being enclosed in a network, or
cage of wires, without the use of the earth. They object to the
application of the laws of static electricity alone to such a case.
Current induction intervenes, and this is not subject to the screening
action of a cage. Hence, though a metallic cage may assist the
protection of a house, it does not do so perfectly.
ON THE PROPER FORM OF LIGHTNING CONDUCTORS. By W. H. PREECE, C.E.
(_British Association Report_, 1880).
(_Abstracted by G. J. Symons, F.R.S._)
Author states that ever since lightning conductors have been used, there
have been disputes as to whether the discharge passes over the surface
of conductors or through their mass. Snow Harris, Henry, Melsens, and
Guillemin have held that it passed over the surface; Faraday held the
opposite view.
The arguments in favour of the surface form are, in the opinion of the
author, deductions from exploded theories, from imperfect experiments,
or from erroneous interpretations of well ascertained facts. No direct
experiments have ever been made to solve the question, as far as the
author knows. Quantities of electricity, that is static discharges from
condensers, are in incessant use for telegraphic purposes, and are found
to follow exactly Ohm’s laws, even with the most delicate apparatus. The
knowledge of the flow of electricity through conductors, of the
retarding influence of electrostatic capacity upon this flow, and of the
distribution of charge, has become so much greater of late years through
the great extension of submarine telegraphy and the labours of Sir
William Thomson, Clerk Maxwell, and others, that the author questions if
any English electrician would now be found to argue in favour of the
surface form. Nevertheless, as ribbons and tubes still continue to be
used, and it appeared very desirable to settle the question
experimentally, the author determined to try and do so.
_First Experiments, June 28, 1880._
Dr. Warren de la Rue, who is always ready to place his splendidly
equipped laboratory at the service of science, not only allowed the
author to use his enormous battery and his various appliances, but aided
him by his advice, and assisted him in conducting the experiments.
Copper conductors, 30 feet long, of precisely the same mass, (_a_) drawn
into a solid cylinder, (_b_) made into a thin tube, and (_c_) rolled
into a thin ribbon, were first of all obtained. The source of
electricity was 3,240 chloride of silver cells. The charge was
accumulated in a condenser of a capacity of 42·8 microfarads. It was
discharged through platinum wire of ·0125 diameter, of different
lengths. The sudden discharge of such a large quantity of electricity as
that contained by 42·8 mf. raised to a potential of 3,317[5] volts is
very difficult to measure. It partakes very much of the character of
lightning. In fact, the difference of potential per unit length of air
is probably greater than that of ordinary lightning itself. It
completely deflagrates 2½ inches of the platinum wire, but by increasing
the length of the wire it could be made to reproduce all the different
phases of heat which are indicated by the various shades of red until we
reach white heat, fusion, and deflagration. Hence the character of the
deflagration, which is (by its scattered particles) faithfully recorded
on a white card to which the wire is attached, is a fairly approximate
measure of the charge that has passed, while the length of wire, raised
to a dull red heat, is a better one, for any variation in the strength
of the current within moderate limits is faithfully recorded by the
change of colour.
Footnote 5:
The electromotive force of the chloride of the silver cell is 1·03
volt.
Experiment 1.—Similar charges were passed through the ribbon, tube, and
wire, and in each case 2½ inches of wire were deflagrated. No difference
whatever could be detected in the character of the deflagration.
Experiment 2.—Ten inches of wire were taken and similar charges passed
through. In each case the wire was raised to very bright redness,
bordering on the fusing point, and in two cases the wire broke. In each
case the wire knuckled up into wrinkles, and gave evidence of powerful
mechanical disturbance. The same wire was not used a second time. No
difference could be detected in the effect through the different
conductors.
Experiment 3.—Silver wire of the same diameter and length was used, and
similar charges transmitted through it. Redness was barely visible, but
the behaviour of the wire was similar in each case.
The conclusion arrived at unhesitatingly was, that change of form
produced no difference whatever in the character of the discharge, and
that it depended simply on mass.
_Second Experiments, July 19, 1880._
As it might be urged that the length of conductor tested was so short,
and its resistance so small that considerable variations might occur and
yet be invisible, similar lengths (30 feet) of lead—a very bad
conductor, its resistance being twelve times that of copper—were
obtained, drawn as a wire, made as a tube, and rolled as a ribbon, each
being of similar weight.
Experiment 4.—Charges from the same condenser, 42·8 mf., but with 3,280
cells, were passed through, and the discharges observed on 6 inches of
platinum wire 0·0125 inch diameter, which in each case was heated to
bright redness. No variation whatever could be detected, whether the
wire, the tube, or the ribbon were used.
Experiment 5.—In order to form some idea as to how closely any variation
in the character of the discharge could be estimated, a long piece of
platinum wire was used, and the length adjusted until just visible
redness was obtained; then a diminution of 10 per cent. (3 feet)
produced a marked change to dull redness, and further excisions raised
the temperature to brighter and still brighter red.
The conclusion arrived at was that any change in resistance of 5 per
cent. would have been clearly and easily discernible.
It therefore appears proved that the discharges of electricity of high
potentials obey the laws of Ohm, and are not affected by change of form.
Hence, extent of surface does not favour lightning discharges. No more
efficient lightning conductor than a cylindrical rod or a wire rope can
therefore be devised.
ÉTABLISSEMENT DE LA FORMULE RELATIVE AU RAYON D’ACTION DES
PARATONNERRES. Par EMILE LACOINE. (_L’Electricité_, October, 1880.)
(_Abstracted by G. J. Symons, F.R.S._)
This author gives a formula for determining the area protected, which he
considers to vary with the height of the storm cloud, and the elevation
of the ground. He states that the mean elevation of the storm clouds at
Constantinople is as low as about 325 feet. He says that conductors
placed near the extremities of a building have their radius of
protection diminished, and therefore recommends a line conductor running
round the building. (The _circuit des faites_ of the Paris Municipal
Commission, see ante page 68).
He says that his formula leads to nearly the same results as have
hitherto been adopted, but he gives three examples, the results of which
are—length of conductor being 1·00, radius protected is respectively
3·80, 1·10, and 2·20.
ON THE SPACE PROTECTED BY A LIGHTNING CONDUCTOR. By W. H. PREECE, C.E.
(_Phil. Mag._, Dec., 1880.)
(_Abstracted by G. J. Symons, F.R.S._)
In the early part of this paper the author discusses the distribution of
electricity in the space between the storm cloud and the earth’s
surface, and points out that the air in an electric field is in a state
of tension or strain; and this strain increases along the lines of force
with the electromotive force producing it until a limit is reached, when
a rent or split occurs in the air along the line of least
resistance—which is disruptive discharge, or lightning.
Since the resistance which the air or any other dielectric opposes to
this breaking strain is thus limited, there must be a certain rate of
fall of potential per unit length which corresponds to this resistance.
It follows, therefore, that the number of equipotential surfaces per
unit length can represent this limit, or rather the stress which leads
to disruptive discharge. Hence we can represent this limit by a length.
We can produce disruptive discharge either by approaching the
electrified surfaces producing the electric field near to each other, or
by increasing the quantity of electricity present upon them; for in each
case we should increase the electromotive force and close up, as it
were, the equipotential surfaces beyond the limit of resistance. Of
course this limit of resistance varies with every dielectric; but we are
now dealing only with air at ordinary pressures. It appears from the
experiments of Drs. Warren de la Rue and Hugo Müller that the
electromotive force determining disruptive discharge in air is about
40,000 volts per centimetre, except for very thin layers of air.
If we take into consideration a flat portion of the earth’s surface, and
assume a highly charged thunder-cloud floating at some finite distance
above it, they would, together with the air, form an electrified system.
There would be an electric field; and if we take a small portion of this
system, it would be uniform.
If the cloud gradually approached the earth’s surface, the field would
become more intense, the equipotential surfaces would gradually close
up, the tension of the air would increase until at last the limit of
resistance of the air would be reached; disruptive discharge would take
place, with its attendant thunder and lightning.
[Illustration:
Fig. 1.
]
If the earth-surface be not flat but have a hill or a building, as A or
B, upon it, then the lines of force and equipotential planes will be
distorted, as shown in fig. 1. If the hill or building be so high as to
make the distance HD equal to the limit of resistance (fig. 2), then we
shall again have disruptive discharge.
[Illustration:
Fig. 2.
]
If instead of a hill or building we erect a solid rod of metal, G H,
then the field will be distorted as shown in fig. 2. Now it is quite
evident that whatever be the relative distance of the cloud and earth,
or whatever be the motion of the cloud, there must be a space _d d´_
along which the lines of force must be longer than _c c´_ or H D; and
hence there must be a circle described around G as a centre which is
less subject to disruptive discharge than the space outside the circle;
and hence this area may be said to be protected by the rod G H. The same
reasoning applies to each equipotential plane; and as each circle
diminishes in radius as we ascend, it follows that the rod virtually
protects a cone of space whose height is the rod, and whose base is the
circle described by the radius G _c_. It is important to find out what
this radius is.
[Illustration:
Fig. 3.
]
Let us assume that a thunder-cloud is approaching the rod A B (fig. 3)
from above, and that it has reached a point D´ where the distance D´ B
is equal to the perpendicular height D´ C´. It is evident that if the
potential at D´ be increased until the striking-distance be attained,
the line of discharge will be along D´ C´ or D´ B, and that the length A
C´ is under protection. Now the nearer the point D´ is to D the shorter
will be the length A C´ under protection; but the minimum length will be
A C, since the cloud would never descend lower than the perpendicular
distance D C.
Supposing, however, that the cloud had actually descended to D when the
discharge took place. Then the latter would strike to the nearest point;
and any point within the circumference of the portion of the circle B C
(whose radius is D B) would be at a less distance from D than either the
point B or the point C.
“_Hence a lightning-rod protects a conic space whose height is the
length of the rod, whose base is a circle having its radius equal to the
height of the rod, and whose side is the quadrant of a circle whose
radius is equal to the height of the rod._”
Upon this rule the author makes the following concluding remarks:
“I have carefully examined every record of accident that I could
examine, and I have not yet found one case where damage was inflicted
inside this cone when the building was properly protected. There are
many cases where the pinnacles of the same turret of a church have been
struck where one has had a rod attached to it; but it is clear that the
other pinnacles were outside the cone; and therefore, for protection,
each pinnacle should have had its own rod. It is evident also that every
prominent point of a building should have its rod, and that the higher
the rod the greater is the space protected.”
SHORT ACCOUNT OF THE STRIKING BY LIGHTNING OF THE RAILWAY TERMINUS AT
ANTWERP, ON THE 10TH OF JULY, 1865. BY M. MELSENS, Member of the Royal
Academy of Belgium.
(_Abstracted by R. Van der Broek._)
On the date mentioned, between three and four o’clock in the afternoon,
a violent storm burst over Antwerp, during which the lightning struck
the Railway Terminus, without, however, occasioning any other damage
than the perforation of a single hole in one of the glass squares of the
roof.
The author states that the effect of the discharge on this square of
glass, which was about 4^{mm} (0·2in.) thick, was remarkable; it
appeared as if it had been traversed by a projectile from below, the
perforation, viewed from above, being broken and chipped, whilst viewed
from below it showed a clean edge. The sinuosities caused by the
chipping on the upper surface had rounded edges, and the glass appeared
to have been subjected to incipient fusion. Not a single fragment of
glass was found on the glass squares or in the gutters of the roof.
The author arrives at the following conclusions: The square of glass was
pierced in the same manner as any square of similar nature and
dimensions, placed in identical circumstances, would be, were it
traversed by a spherical projectile fired at a low velocity from a
firearm. The fracture resembled one that would be produced by a missile
thrown from below, that is to say, from the earth to the sky.
The form of the opening indicated that the earth was positively
electrified.
The author notices that, according to M. F. Duprez, negative electricity
generally shows itself in abnormal conditions of the atmosphere, during
storms, rains, &c., and when the wind blows from the western quarters
between N. and S. Now, on the day in question, it rained and the wind
blew from the west.
The author publicly thanks M. Ruhmkorff for his skilful and
disinterested co-operation in proving the correctness of his (the
author’s) view of the distribution of the electricity at the Antwerp
discharge. M. Ruhmkorff has, at request, pierced squares of ordinary
glass about 1^{mm} (0·04in.) thick by the discharge of his great
induction apparatus charged by a powerful Leyden battery.
ON LIGHTNING PROTECTORS WITH POINTS, CONDUCTORS, AND MULTIPLE EARTH
CONNECTIONS, A DETAILED DESCRIPTION OF THE LIGHTNING PROTECTOR ERECTED
ON THE TOWN HALL OF BRUSSELS IN 1865, WITH AN ACCOUNT OF THE PRINCIPLES
ADOPTED IN THE CONSTRUCTION, BY M. MELSENS, MEMBER OF THE ROYAL ACADEMY
OF SCIENCES OF BELGIUM.
(_Abstracted by R. Van der Broek._)
As the author states in his preliminary observations that it is
impossible to give a complete condensed description of the Lightning
Protector, which he erected on the Town Hall at Brussels, we will merely
draw attention to a number of facts, regarding the system followed, some
of them, we believe, of a novel description.
M. Daniel Colladon, the author states, has observed that as a rule
lightning does not strike a single part or prominent point of the
objects that are struck or destroyed by it; and that, in the majority of
cases, it does not strike in the form of a single spark, but in the form
of a sheet with one or more principal centres of intensity. The
correctness of this observation, the author considers fully borne out by
the ravages which the electric discharge committed on the Town Hall at
Brussels, on the 10th September, 1863. He gives an elaborate description
of the effects of the flash on the building. It is interesting to note
that the ravages principally took place at the side exposed to the west
north-west wind, which was blowing at the time the building was struck.
In the ensuing winter the Municipal Council of Brussels took into
consideration the necessity of protecting the Town Hall against a
similar disaster, and the author was requested to superintend the
erection of lightning protectors on the building.
The characteristics of the author’s system, as exemplified by the
lightning protectors erected on the Brussels Town Hall, may be briefly
summarised as follows:—
1. The points are very numerous—of three kinds; some long, sharp, and
gilded, others of middling length, made of iron; and finally some
small and very sharp, consisting of copper.
2. The points are replaced by _aigrettes_ (brushes of points diverging
from a common base).
3. The conductor is not insulated.
4. The connections are simple and unchangeable, the joints are each
embedded in a mass of zinc.
5. The surface exposed to the air is considerable.
6. The conductor consists of thin, and numerous wires, which are very
flexible, so as easily to be led round all the corners of the
buildings.
7. The conductor is made of galvanised iron.
8. The earth connections are multiple: firstly, a well within which a
large surface of metal is plunged; and, secondly, two enormous
networks of metal pipes, offering an immense contact surface with
the earth. One of these networks is in direct communication with
all the reservoirs and all the water sources of the environs of
Brussels and also in indirect communication with two rivers and
two canals.
The author has arrived at the conclusion that the height of the rod is a
secondary question, as the radius of protection has not been determined
by irrefutable proofs, and as that length is, in comparison with the
distance and the extent of the thunder-clouds, so small a factor that it
may safely be neglected. The author states that he has been greatly
gratified to meet with the same opinion in a paper which Mr. W. H.
Preece published in Vol. I., No. 3, page 366, of the Journal of the
Society of Telegraph Engineers for 1872: “When we consider the distance
of the cloud and the area of its surface, the height of a building
vanishes in the general figure.”
The author points out that M. Perrot has endeavoured to demonstrate by
experiment that the neutralizing area of a lightning protector
surmounted by a crown of sharp points is far more extensive than that of
an ordinary protector. M Perrott further thought, and MM. Babinet and
Gavarret shared his opinion, that it is sufficient to shelter the
ordinary protector from discharges of lightning by arming it with
numerous, long, sharp, and well conducting divergent points. M. Gavarret
after having repeated Mr. Perrott’s experiments, found the results so
conclusive that he wrote to the author in the beginning of 1865: “It is
at the present time no longer permitted to erect lightning protectors
with single points.”
The metal of which the points are made must be a very good conductor.
With regard to their conductivity, the metals follow each other in the
following order: copper, silver, iron, platinum. No metals are used but
those which resist fusion. The author rejected platinum and silver: the
former because it fuses very readily by the electric discharge; and the
latter, because it has, in his opinion, no advantage over copper.
The conductor, although galvanized, received several coats of paint; but
the points (_aigrettes_) of course remained metallic. With regard to the
general principle of connecting the protector with any masses of metal
which may be about the building, the author has ever since 1865
endeavoured to demonstrate, that it is not sufficient, as might at first
sight be supposed, to form that connection at one single point; there
must be at least two points of contact, so as always to ensure a closed
metallic circuit.
The contact with the water presents a surface of about ten square metres
(12 sq. yds.), bringing both surfaces of the cylinder into account.
With regard to the earth connection, the author quotes M. Perrot, who
remarks that with the ordinary protector the surface immerged offers a
resistance at least 10,000 times greater than the conductor itself; it
is therefore necessary to increase the surface of the earth-plate as
much as possible.
In order to retard as much as possible the oxidation of the cylinder,
the author introduced two hectolitres (6 bushels) of lime into the well,
thus rendering the water alkaline.
DE L’APPLICATION DU RHE-ÉLECTROMÈTRE AUX PARATONNERRES DES TÉLÉGRAPHES.
PAR M. MELSENS.
(_Abstracted by R. Van der Broek._)
In this pamphlet the author describes in § 1 an apparatus to show the
presence of atmospheric electricity in telegraph wires.
In §§ 2 and 4 he explains how the apparatus is joined up in the Belgian
telegraph offices.
§ 3 contains a résumé of observations made at the government telegraph
offices between June, 1875, and March, 1876.
The author states in this paragraph that, on the 19th of June, 1875, the
Rheo-Electrometer at the office at Louvain, showed a deflection of 85°
East, although there was not the slighest appearance of atmospheric
electricity. The fact was, that at the time a thunder storm was raging
at Beverloo, distant from Louvain about 40 kilometres (25 miles).
TROISIÈME NOTE SUR LES PARATONNERRES. PAR M. MELSENS.
(_Abstracted by R. Van der Broek._)
On the 3rd of July, 1874, the church of Ste. Croix, at Ixelles, was
struck by lightning. The building was provided with a lightning
protector, which was constructed as follows: The point consisted of a
platinum cone of about 30° (the form officially adopted in France in
1855), all the supports of the protector were soldered with zinc. This
was attached to the steeple, and rose to 53 metres or 174 feet above the
pavement. It consisted of an iron rod 18 mm. (0·71 in.) in diameter (M.
E. Sacré’s system). The conductor passed from the principal roof along
the roofs, descending to a point near a pump, behind the vestry, where
the well (W) was situate. There is an abundance of water in the well,
which is about 7 m. (23 ft.) deep. The conductor terminated in the well,
by a cast-iron plate 0·65 m. (2 ft. 1 in.) by 0·50 m. (1ft. 8 in.), thus
presenting a surface of 0·654 ⬜ m. (7 sq. ft.). A little in front of the
transept there is a supplementary rod B 5·25 m. (17 ft. 3 in.) high, 11
m. (36 ft.) distant from the point (c in diagram) which was struck; and
22 m. (72 ft.) distant from that point there was a second rod D, whose
height was 9 m. (29½ ft.) above the top of the roof.
The damage to the church was trifling, but the author contends that the
fact of the church having been struck at all, proves that a building
armed with a protector constructed on the usual principle is not
completely protected.
[Illustration: Plan and Elevation of Church of Ste. Croix, at Ixelles]
A. Principal conductor on steeple.
B. D. Two supplementary receiving rods.
C. Stone cross at end of transept, which was struck,
W. Well in which conductor made earth connection.
QUATRIÈME NOTE SUR LES PARATONNERRES. PAR M. MELSENS.
(_Abstracted by R. Van der Broek._)
This treats § 1 of observations on the distribution of the spark of
electric batteries and machines over numerous metallic conductors of
different sections, lengths, and nature, and on the passage of
electricity of tension in bad conductors.
§ 2. Effects of soldered joints on the conductivity and the resistance
of conductors. Interrupted lightning protectors.
§ 3. The distribution of sparks from Holtz’s machine and Ruhmkorff’s
coil over two conductors outwardly identical, but one of iron and the
other of copper. Comparative resistance to fusion and rupture for iron
and copper conductors. Identical damage produced by discharges in
several homogeneous and solid conductors.
APPENDIX G.
CATALOGUE OF WORKS UPON LIGHTNING CONDUCTORS,
WITH A FEW UPON
LIGHTNING, THUNDER, AND THE EFFECTS OF LIGHTNING STROKES,
_Chiefly extracted from the_ RONALD’S CATALOGUE, _edited by Mr. Frost,
but supplemented and brought down to 1880 by extracts from the
Catalogues of_
R. ANDERSON, F.C.S.; LATIMER CLARK, C.E.; and G. J. SYMONS, F.R.S.
There are not many comments needed upon the following catalogue, but a
few are necessary.
The arrangement is, with one exception, strictly alphabetical under
author’s names; that exception being that all the Official Instructions
issued in France are placed together at the beginning of the catalogue.
The initials =R=, =C=, =A=, =S=, are those of the Catalogues or
Libraries in which the works are to be found; small type indicates that
the title of the work is given in the catalogue indicated; large type
that a copy of the book is in that Library. As Mr. Anderson does not
state distinctly whether he possesses the books or has merely their
titles, it has been thought safer to mark those taken from his catalogue
with the small ¤A¤. The existence of any specified work in a certain
library is absolute proof of the existence of the book, and hence the
larger type has a certain value, and, besides that, I purpose,
immediately after the publication of this Report, presenting to the
Society of Telegraph Engineers all the Electrical works which are in my
library but are not in the Ronald’s Library. It may therefore be assumed
that most of the works to which a large type initial is prefixed are, or
soon will be, in the splendid collections of the Society of Telegraph
Engineers and Electricians.
The small figures in the front column show the pages of Appendix F, upon
which abstracts of upwards of fifty of the following works will be
found—and thus it forms an index to the works abstracted.
G. J. S.
OFFICIAL INSTRUCTIONS, FRANCE.
(_Abstracts of this series will be found on pages 51–69._)
=R= =S= │Instruction sur les Paratonnerres pour
│ servir à l’Etablissement de ces Appareils
│ au-dessus des Magasins à poudre, adoptée
│ par le Comité des Fortifications dans sa
│ Séance du 25 Août 1807: suivie des
│ Rapports faits à ... l’Institut et à
│ l’Académie des Sciences, sur cette
│ Instruction et sur l’Etablissement des
│ Paratonnerres en général. Fol. 39 pp. 1
│ plate. _Paris_, =1808=
│ (This paper contains the reports by
│ Franklin and others, dated 24th
│ April, 1784; by Leroy and others,
│ dated 27th December, 1799; and by La
│ Place and others, dated 2nd November,
│ 1807.)
│
¤R¤ │Instruction sur les Paratonnerres. Fol. _Paris_, =1823=
│
=R= │Instruction sur les Paratonnerres adoptée
│ par l’Académie, 23 April, 1823, (Signé)
│ Poisson, Lefevre-Gineau, Dulong, Fresnel,
│ et Gay-Lussac rapporteur. 4to. 51 pp. 2
│ plates. _Paris_, =1824=
│
=S=│Instruction sur les Paratonnerres adoptée
│ par l’Académie Royale des Sciences le 23
│ Juin, 1823. 8vo. 51 pp. 2 plates. _Paris_, =1824=
│
=R= =S= │Supplément à l’Instruction sur les
│ Paratonnerres, présenté par la section de
│ physique. MM. Becquerel, Babinet,
│ Duhamel, Despretz, Cagniard de Latour,
│ Pouillet rapporteur. 4to. _Ext. des
│ Comptes Rendus_, tom. xxxix. 112, and
│ xl., Séance 18 Déc. 1854. _Paris_, =1854–5=
│
=R= ¤S¤ │Instruction sur les Paratonnerres adoptée
│ par l’Acad. des Sciences. 12mo. 130 pp.
│ Cuts. _Paris_, =1855=
│
=R= ¤S¤ │Instruction sur les Paratonnerres des
│ magasins à poudre. Rapport lu 14 Janv.,
│ 1867. Commissaires Becquerel, Babinet,
│ Duhamel, Vaillant, Pouillet, Fizeau,
│ Regnault. 4to. 1 plate. 15 pp. (_Ext. des
│ Comptes Rendus_, tom. lxiv. Séance 21
│ Janv. 1867.) _Paris_, =1867=.
│
=S=│Instruction sur les Paratonnerres du Louvre
│ et des Tuileries. (_Ext. des Comptes
│ Rendus_, tom. lxvii. Séance 20 Juillet,
│ 1868). 4to. _Paris_, =1868=
│
¤A¤ =S=│Instruction sur les Paratonnerres adoptée
│ par l’Acad. des Sciences. Part I., 1823,
│ M. Gay Lussac, rapporteur; Part II.,
│ 1854, and Part III., 1867, M. Pouillet,
│ rapporteur. 12mo. _Paris_, =1874=
│
Met. Soc.│Analyse des Rapports de M. de Fonvielle, à
│ la suite de la mission qui lui avait été
│ confiée en 1872, par M. Jules Simon, pour
│ faire en Angleterre une enquête sur la
│ foudre et les Paratonnerres. Fcap. fol. _Paris_, =1875=
│
Met. Soc.│Analyse des Rapports des Architectes sur
│ l’Etat des Fcap. fol. _Paris_, =1875=
│
Met. Soc.│Instruction de la Commission chargée
│ d’étudier l’établissement des
│ paratonnerres des Edifices Municipaux de
│ Paris, adoptée dans la Séance du 20 Mai,
│ 1875. Fcap. fol. _Paris_, =1875=
│
Met. Soc.│Résumé des expériences faites à
│ l’Administration des Lignes
│ Télégraphiques sur les parafoudres
│ télégraphiques. Fcap. fol. _Paris_, =1875=
ANONYMOUS.
(_Arranged chronologically._)