outside of a jar with tin foil, applying the charge by means of a wire
or chain to the inside coating and allowing the outer one to stand
upon the earth or upon a conducting substance in electrical contact
with the latter. The exaltation of spirit with which the discovery was
hailed by the _savants_ appears to have been extraordinary--one
student who took a discharge through his body being reported to state
that he would not have missed the experience for a fabulous
consideration, and that he would not repeat it if it were to save his
life. In reality the advance was enormous; it gave a means for
literally bottling up electricity in quantities previously unthought
of. The prime conductor of an electrical machine could not retain any
considerable quantity of electricity for the reason that, a certain
small intensity of electrification having been reached, the addition
operated to upset the balance, so to speak, and the electricity
escaped by a sudden (disruptive) discharge, or spark, or by the brush
discharge already alluded to. With the Leyden jar, however, as fast as
electricity was supplied to the inside coating it became "bound" there
by the charge of opposite sign accumulating on the outside, and the
limit of capacity of the jar was simply one of strength of the glass:
if too much electricity was supplied, the stress of mutual attraction
between the two charges relieved itself by destroying the jar.
Although Professor Muschenbroeck discovered the principle in the
manner above referred to, it appears extremely probable that two other
investigators, working independently, also did the same. One Cuneus
and a monk named Kleist each claimed the honor of original invention
of the condenser.
About 1747 the first gun was fired by electricity; this was
accomplished by Sir William Watson, who also succeeded in kindling
alcohol and gas by means of a drop of cold water and even with ice.
The same experimenter reversed the ordinary procedure of causing the
electric influence to pass from an electrified body to the one to be
experimented upon, the latter being unelectrified, by electrifying the
latter, and then producing the desired effect by approaching it to an
unelectrified one.
A party of the Royal Society with Watson as chief operator instituted
a series of researches on a grand scale to determine, if possible, the
velocity of the electric discharge, and arrived at a number of
conclusions which, however, were of a decidedly negative nature. The
most important of these were as follows: That they could not observe
any interval between the instant of applying the discharge to one end
of the line and its reception at the other; that the destructive
effects of discharge are greater through bad conductors than through
good ones; that conduction is equally powerful whether occurring
through earth or water.
Just previous to this there had been some brilliant experiments
carried on in France, and the discharge had been conveyed through
twelve thousand feet of circuit, including the acre basin of the
Tuileries, but they had not been performed as systematically, or with
the definite objects in view, as had the English experiments.
The following year the Royal Society continued its researches on a
larger scale than previously, using 12,276 feet of wire, and found
that even through that length the velocity was practically
instantaneous.
Watson urged as a theory that electrical disturbances were caused by
influx or efflux of a single electric fluid from the state of normal
electrification, thus differing from Dufay in his opinion as to the
existence of two fluids. He was led to this belief by observing that
he obtained a larger spark between two oppositely electrified bodies
than from either to the earth.
From this time on there appears upon the scene a host of workers in
this field, one of the most prominent being the distinguished
American, Benjamin Franklin. Somewhat previous to his remarkable work,
or about 1750, Boze made certain discoveries in the matter of the
surface tension of conducting liquids being diminished by
electrification, and Mowbray and Nollet ascertained that the
vegetation of flowers and of vegetating seeds was hastened by
electrifying them.
Franklin (born 1706, died 1790) made the important discovery of the
active discharge of electricity from an electrified body by points as
well as the converse of it--i. e., that electricity was rapidly
abstracted from a charged atmosphere by points. This enabled him to
increase the efficiency of the electrical machine by adding a
comb-shaped series of points to the collector of the prime conductor.
Up to this time, although the identity of lightning with electricity
had long been suspected, it had not been at all established, and to
Franklin may be said to belong the honor of doing so, although in
this, as in the case of the invention of the Leyden jar, there appears
to have been successful contemporaneous research elsewhere. Before
performing his great experiment Franklin published a book strongly
supporting the belief in the identity of the two. Once having
conceived the idea of drawing electricity from the upper atmosphere,
he unfortunately lost some time through waiting for the completion of
the spire of a certain church in Philadelphia, from the top of which
he hoped to be able to collect electricity by means of a wire, but
finally hit upon the device which now fills much the same place in
connection with his memory that the classical cherry tree does with
Washington's--the lightning-collecting kite. This apparatus was very
simply constructed, and had a pointed wire projecting a short distance
above the framework. It was controlled, and electrical connection
made, by an ordinary string which terminated in a short length of silk
ribbon to protect the person from possible injury, and to give
electricity a chance to accumulate in the system, by insulating the
"line." At the end of the string proper Franklin fastened a metallic
key. In company with his son he flew the kite during a thunderstorm
which occurred in June, 1752; for some time no electric disturbance
approached the neighborhood, and he was on the point of abandoning the
experiment when he observed what he had been waiting for--the outer
fibers of the string standing out from the latter by repulsive
force--and, applying his knuckle to the key, he drew a spark.
Subsequently, when the rain soaked the string and caused it to conduct
much better, there was a fine supply of electricity, and Franklin
charged a Leyden jar from the key, thus achieving the actual storage
of "lightning."
He continued his investigations in atmospheric electricity, and
discovered that the electrification of the clouds (or of the upper
atmosphere) was sometimes positive and sometimes negative. The
invention of the lightning rod is due to him.
Franklin sided with Watson in his belief in the single nature of the
electric fluid.
As intimated above, atmospheric electricity appears to have been
collected independently about the same time in Europe, and certain
very daring and dangerous experiments were performed there. One sad
occurrence, as a result, was the death of Professor Richman, in St.
Petersburg, in 1753. Richman, in company with a friend, Sokolow, was
taking observations on an electroscope connected with an iron rod
which terminated in the apartment and extended in the other direction
above the roof of the building. During the progress of their
experiments a violent peal of thunder was heard in the neighborhood,
and Richman bent to examine the instrument. In doing so he approached
his head to within a foot of the end of the rod, and Sokolow saw a
ball of fire "about the size of a man's fist" shoot from it to
Richman's head with a terrific report. The stroke was, of course,
immediately fatal, and what we now know as the return shock stupefied
and benumbed Sokolow. The unfortunate event served as a warning to
other daring experimenters.
Canton, another prominent worker in this field, discovered that the
so-called vitreous electricity was not necessarily always developed by
the friction of glass, as had hitherto been believed to be invariably
the case. By applying different rubbers to glass he obtained either
positive or negative at pleasure. This at once disposed of the idea
that one kind of electricity resided in certain bodies and its
opposite in others. Canton also made the interesting discovery that
glass, amber, rock crystal, etc., when taken out of mercury, were all
electrified positively. He was thus enabled to make the improvement in
the electrical machine of coating its rubber with an amalgam rich in
mercury, which greatly enhanced its powers.
Among the numerous names now coming into prominence must be mentioned
those of Beccaria, Symmer, Delaval, Wilson, Kinnersley, Wilcke, and
Priestley.
The first named, Father Beccaria, was a celebrated Italian physicist
who did most valuable work in connection with atmospheric electricity,
and who published several classical works on that and allied subjects.
Among these may be mentioned his _Lettre del Elettricità_, 1758, and
_Experimenta_, 1772. He ascertained that water is not by any means a
good conductor, as it had previously been supposed to be, and, by
using pure water, he caused the electric spark to become visible in
it, a phenomenon capable of occurring only through media almost
nonconducting. In these experiments he used thick glass tubes with
wires led through the opposite ends, the latter being sealed, and the
tubes filled with water. These were invariably shattered by the
passage of the spark on account of the accompanying elevation of
temperature, which caused expansion. He also established the facts
that the atmosphere adjacent to an electrified body acquires
electrification of the same sign by abstracting electricity from the
body, and that the air then parts with its electricity very slowly. He
advanced the theory that there is a mutual repulsion between the
particles of the electric fluid and those of air, and that a temporary
vacuum is formed at the moment of the passage of a disruptive
discharge or spark.
Robert Symmer, in 1759, described some most entertaining experiments,
making use of the opposite electrifications of superposed stockings of
different materials or merely of different colors (the dye matters in
the latter case causing differentiation). If, in a dry atmosphere, a
silk stocking be drawn over the leg and a woolen one pulled over it,
the two will be found, upon being removed, to be very powerfully
electrified in opposite senses. If the four stockings of two such
pairs be used and then suspended together, they will indulge in
remarkable antics due to each of the silk stockings trying to attract
both of the woolen ones, and _vice versa_, and, on the other hand,
each of each kind repelling the other. The amount of electrical
attraction and repulsion produced in this simple way in a dry
atmosphere is remarkable. The experiment may also be performed with
all silk stockings, one pair white and the other black.
Symmer advanced the theory of two fluids coexisting in all matter (not
independently of each other, as had been previously supposed), which
by mutual counteractions produced all electrical phenomena. His
conception was that a body, positively electrified, did not exist in
that condition because of the possession of a charge of a positive (as
distinct from a negative) electric fluid which it had not held before,
and did not hold in a normal state; nor that it possessed a greater
share of a single electric fluid than it did in an unelectrified
condition, as had been believed by Franklin and Watson, and by Dufay
respectively; but that such a body contained both positive
and negative electricities which, when the body behaved as
"unelectrified," entirely counteracted each other, but which, on the
other hand, caused a positive or negative charge to be evinced should
either positive or negative electricity respectively preponderate.
Æpinus was the author of another notable theory, of which we must omit
further mention for want of space.
Disjointed observations connected with animal electricity had been
accumulating for many centuries. The first chronicled note that refers
to the subject dates back to 676 A. D. Whether or not entirely by
chance, the Arabians named the electric eel, or torpedo, in a way that
impresses us now as singularly felicitous, _raad_ (the lightning).
Toward the end of the last century Redi discovered that the shock was
sometimes conveyed through the line and rod to the fisherman, and
Kampfer compared the effects to those of electrical discharges. It
does not appear, however, that the resemblance was actually believed
to be more than accidental until Bancroft urged, in the last ten years
of the eighteenth century, the view which was shortly proved.
Investigation since has shown that several other aquatic animals
possess this astonishing manifestation of vitality, notably the
_Gymnotus electricus_ (Surinam eel), the _Trichiurus electricus_, and
the _Tetraodon electricus_. Humboldt gives an account of wonderful
battles in South America between gymnoti and wild horses. In fact, the
most expeditious method, if not the most humane one, of capturing
these alarming creatures appears to be to drive horses into the pond
inhabited by them, and to allow the eels to exhaust their strength by
repeated electric discharges before endeavoring to bring them to land
by other means.
Cavendish was one of the most noted experimental investigators in the
electrical field during the latter third of the eighteenth century.
His work was remarkably accurate, considering the lack of a proper
equipment for taking observations incident to operations in those
days. He computed the relative conductivities of iron and water as
four hundred million to unity, and found that the addition of but one
part of common salt to one hundred of water increased the conductivity
of the latter a hundredfold. A twenty-six-per-cent solution of salt he
found to possess only seven and one quarter times the conductivity of
the extremely weak one mentioned. He also established the law that the
capacity of condensers (of which the previously mentioned Leyden jar
is an example) varies directly as the active area, and inversely as
the distance separating the conducting surfaces. It was reserved for
later investigators to make the grand discoveries which relate to
electrochemical dissociation, but Cavendish succeeded in accurately
determining the ratio of combination of the elements of water in a
method which superficially suggests the inverse of electrolytic
decomposition--i. e., by inducing the combination of hydrogen and
oxygen by the electric spark in the instrument known as the
eudiometer.
Hard on the heels of this work came news of Galvani's remarkable
discovery (1790) of the fact that freshly amputated frogs' legs, on
being touched along the lines of the muscles by dissimilar metals,
were powerfully agitated. We can only speak of this discovery as the
stumbling on to an isolated fact, for it was reserved for Volta to
establish the generalization that a current is produced in the
conductor joining dissimilar metals when the latter are both in
contact with a suitable electrolyte (or liquid capable both of
conducting electricity and of acting on one, and incidentally also
sometimes both, of the metals). Meantime (Du Bois-Reymond observes),
"wherever frogs were to be found, and where two different kinds of
metal could be procured, everybody was anxious to see the mangled
limbs of frogs brought to life in this wonderful way. Physiologists
believed that at last they should realize their visions of a vital
power, and physicians that no cure was impossible."
Volta first discovered merely the fact of electrification by contact.
He wrote to Galvani: "I don't need your frog. Give me two metals and a
moist rag, and I will produce your animal electricity. Your frog is
nothing but a moist conductor, and in this respect it is inferior to
my wet rag!" Nobili, nevertheless, in 1825 proved the existence of
galvanic currents in muscles.
Later on Volta invented the "_couronne des tasses_" (crown of cups),
thus at the same time adopting the general form of cell used, with
modifications, to-day, and producing the higher electromotive force,
or electrical pressure, consequent on the multiplication of the cells
in a series battery.
Just before Volta's celebrated communication to the Royal Society, in
1800, Fabroni, of Florence, in discussing Galvani's phenomenon, went
to the root of the matter by suggesting that the energy of chemical
action was at the bottom of galvanic manifestations, and he was warmly
upheld in this contention by Sir Humphry Davy, who, upon the
publication of Volta's discoveries, constructed a most elaborate
battery with which (apparently about 1806) he produced the arc light
between carbon pencils.
In the year referred to, Davy published the results of a series of
experiments of enormous significance, among other things of the
isolation of the alkali metals, sodium and potassium, whose existence
had hitherto not been dreamed of. The simple electrolytic
decomposition of water had been accomplished by Nicolson and Carlisle
in the last year of the eighteenth century. Sir W. S. Harris says: "A
series of new substances was speedily discovered, the existence of
which had never before been imagined. Oxygen, chlorine, and acids were
all dragged, as it were, to the positive pole, while metals,
inflammable bodies, alkalies, and earths became determined to the
negative pole of the battery. When wires connected with each extremity
of the new battery were tipped with prepared and well-pointed
charcoal, and the points brought near each other, then a most intense
and pure evolution of light followed, which on separating the points
extended to a gorgeous arc." It was at first supposed that the
galvanic or voltaic electricity was distinct from the so-called
"frictional" or "ordinary" electricity.
A distinguished contemporary of Cavendish was Coulomb, the value of
whose work in developing certain exceedingly important mathematical
laws with regard to action at a distance, surface densities, and rates
of charge dissipation can hardly be overestimated. His name was given
to the torsion balance which, since his day, has been the standard
instrument for measuring electric and magnetic attractions and
repulsions. The importance of his work has since been recognized by
the perpetuation of his name in connection with the unit of quantity
of electricity, as that of Volta has been honored by its use,
abbreviated (volt), to designate the unit of electrical tension or
pressure.
Certain highly instructive and interesting data were accumulated about
this time by Volta, Laplace, Saussure, and the renowned chemist
Lavoisier, in connection with the subject of electrification produced
when evaporation, and the liberation of gases and vapors in general
from any cause, occurs. The liquid, solid, or mixture liberating the
gas was contained in a metallic dish and the resultant electrification
of the latter examined qualitatively. Volta's observations led him to
conclude that the electrification was always negative, but Saussure
demonstrated finally that its sign was dependent on the material of
the dish. These experimenters covered, between them all, a somewhat
extensive field, examining, among other things, the electrification
resulting from the ebullition of various liquids, from the ordinary
combustion of fuel, and from the decomposition of acids by metals to
liberate hydrogen.
About the end of the first decade of the century Poisson attacked the
phenomena of electricity analytically, and succeeded in demonstrating
the right of electrical investigation to rank among the exact
sciences. Of his most important mathematical propositions is one in
which, assuming as a working hypothesis the existence of two mutually
attracting fluids, he deduced formulæ covering the distribution of
these fluids on the surfaces of two conducting spheres, in or out of
contact.
A great deal of work was done during the end of the last century and
the beginning of the present one on what is now known as
pyro-electrification. The Abbé Haüy discovered that fragments of
tourmaline crystal exhibited opposite electrifications on opposite
extremities of their lines of cleavage. It is this crystal also which
has unusually remarkable powers of polarizing light, and which, under
electro-magnetic stress, suffers modifications of the latter
property. Haüy investigated the field with much diligence, and
succeeded in cataloguing a large number of natural crystals by the
side of tourmaline. The subject was amplified later by Sir David
Brewster, who added a series of artificial crystalline salts to the
list of pyro-electrical materials, among them, notably, hydro-potassic
(and sodic) tartrate. The property was found not always to reside on
these substances, but to be developed by heating them. Brewster found
that even powdered tourmaline exhibited opposite electrifications on
the opposite extremities of each tiny particle, causing the latter to
act, so far as attractions and repulsions went, as infinitesimal
magnets.
Our rapid and imperfect survey has now brought us to the threshold of
the great activity in electrical work elicited by the tremendous
discovery, made by Professor Oersted, of Copenhagen, of the existence
of the electro-magnetic field. It happens that two of the most amiable
and estimable individuals that have ever devoted their lives to
scientific research stand out in this connection head and shoulders
above all other investigators--Ampère and Faraday, the latter sixteen
years younger than the former and destined to long survive him.
WINGLESS BIRDS.
BY PHILIPPE GLANGEAUD.
It is often said that there are no rules without exceptions. We
purpose to test the truth of this maxim once more. Fishes are made to
live in water, but some of them pass the greater part of their
existence in mud. Some even perch upon trees, thus competing with
birds, whose kingdom is the air, and which are able, with the aid of
their wings, to plunge into space and travel rapidly over considerable
distances. Yet there are birds, deprived by Nature, which do not
possess the wing characteristic of the feathered tribe, and are
consequently, like the majority of animals, pinned to the soil.
Birds do not all have equal power of flight, which is closely related
to the extent of the development of their wings. There exist all
grades in the spread of wings between that of the condor, which is
four times the length of the body, whereby the bird is able to rise to
the height of nearly twenty-five thousand feet, and the little
winglets of the auk, which are of no use to it. The penguins have
still smaller wings, which are nothing more than short, flattened
stumps, without proper feathers and covered with a fine, hairlike down
which might be taken for scales.
Another group of birds exists, called appropriately _Brevipennes_,
the wings of which are so poorly developed as to be wholly unsuitable
for flight. As an offset and just compensation for this, their long
and robust legs permit them to run with extraordinary speed. For that
reason they have been called running birds, in distinction from other
kinds that constitute the group of flying birds. Among them are some
gigantic birds, and also some that have no visible wings on the
outside of their bodies, and may therefore be properly called
wingless.
The ostrich is a member of this group. With its bare, callous head and
short bill, its long, featherless neck, and its massive body,
supported by long, half-bare legs, ending in two large toes; its very
short wings, formed of soft and flexible feathers; and its
plume-shaped tail, it presents a very special appearance among the
birds.
The nandous, the American representatives of the ostrich, have still
shorter wings, which have no _remigia_ at all, and terminate in a
horny appendage, and they have no tail feathers.