THE ELECTRIC LIGHT--TORPEDO GUNS--DIVING.
ELECTRIC lights combined with fast steam launches as guard boats
and specially constructed torpedo guns, such as the Nordenfelt and
Hotchkiss machine guns, are at the present time the only _truly
practicable_ means afforded to a man-of-war of defending herself
against the attack of torpedo boats, whether these latter are armed
with the spar, fish, or towing torpedo; the torpedo gun sinking the
boats after the electric light and guard boats have detected their
approach and position.
As has been before stated, nets, shields, booms, &c., placed around
a vessel of war, must, however slightly constructed, affect to a
considerable degree her efficiency, by decreasing her power of moving
quickly in any desired direction, which is essential to the utility of
such a vessel in time of war; and thus on electric lights, guard boats,
and torpedo guns must the safety of ships in future wars really depend,
when attacked by torpedo boats.
_The Electric Light._--The phenomenon of the _Voltaic arc_ was first
discovered by Sir Humphry, then Mr., Davy at the beginning of the
present century. The following is an account of the matter as given by
him in his "Elements of Chemical Philosophy":--
"The most powerful combination that exists, in which number of
alternations is combined with extent of surface, is that constructed
by the subscription of a few zealous cultivators and patrons of
science in the laboratory of the Royal Institution. It consists of
200 instruments, connected together in regular order, each composed
of ten double plates arranged in cells of porcelain, and containing
in each plate thirty-two square inches; so that the whole number of
double plates is 2,000, and the whole surface 128,000 square inches.
This battery, when the cells were filled with sixty parts of water,
mixed with one part of nitric acid, and one part of sulphuric acid,
afforded a series of brilliant and impressive effects. When pieces
of charcoal about an inch long and one-sixth of an inch in diameter
were brought near each other (within the thirtieth or fortieth part of
an inch), a bright spark was produced, and more than half the volume
of the charcoal became ignited to whiteness, and by withdrawing the
points from each other, a constant discharge took place through the
heated air, in a space equal at least to four inches; producing a most
brilliant ascending arch of light, broad, and conical in form in the
middle. When any substance was introduced into this arch, it instantly
became ignited. Platina melted as readily in it as wax in the flame
of a common candle; quartz, the sapphire, magnesia, lime, all entered
into fusion; fragments of diamond, and points of charcoal and plumbago,
rapidly disappeared, and seemed to evaporate in it, even when the
connection was made in a receiver exhausted by the air pump; but there
was no evidence of their having previously undergone fusion."
The philosopher also showed that, when the Voltaic or electric arc is
produced in the exhausted receiver of an air pump, the phenomena are
as brilliant in character, and the charcoal points can be more widely
separated, thus proving that the electric light is quite independent of
the oxygen of the air for its support.
Owing to the crude nature of the Voltaic batteries of that day, and
also to the great expense of maintaining a large battery of that
nature, nothing practical resulted from Davy's discovery of the
electric or Voltaic arc. Professor Faraday, the great physicist, by
his discovery of the principle of magneto-electricity, has enabled
the electric light to be brought into practical use. As early as
1833 Pixii applied the principle practically in the construction of
a magneto-electric machine with revolving magnets; he was followed
by Laxton, Clark, Nollet, Holmes, and others, who made machines with
fixed magnets. In 1854 Dr. Werner Siemens, of Berlin, introduced the
"Siemens' Armature," which, from its compact form, permitted a very
high velocity of rotation in an intense magnetic field, giving powerful
alternating currents, which, when required, were commutated into one
direction.
The latest improvement has been that from the magneto-electric to
the dynamo-electric machine. It is due to both Dr. Siemens and Sir
C. Wheatstone. Induced currents are directed through the coils of
the electro-magnets which produce them, increasing their magnetic
intensity, which in its turn strengthens the induced currents, and so
on, accumulating by mutual action until a limit is reached.
_Siemens' Electric Light._--The following is a description of
Messrs. Siemens Brothers' dynamo-electric light apparatus, which,
for use on board ship against boat torpedo attacks, &c., is equal,
if not superior, to any similar apparatus yet produced, and which
is extensively used in the German and other European navies. This
apparatus was one of many others experimented on by Dr. Tyndal and Mr.
Douglas, M.I.C.E., for the Trinity House.
Dr. Tyndal says: "I entirely concur in the recommendation of Mr.
Douglas, that the Siemens machine recently tried at the South Foreland
be adopted for the Lizard. From the first I regarded the performance of
this handy little instrument as wonderful. It is simple in principle,
and so moderate in cost that a reserve of power can always be
maintained without much outlay. By coupling two such machines together,
a great augmentation of the light is moreover obtainable."
_Principle._--When a closed electrical circuit is moved in the
neighbourhood of a magnetic pole, so as to cut the lines of magnetic
force, a current is generated in the circuit, the direction of which
depends upon whether the magnetic pole is N or S; it also depends on
the direction of motion of the circuit, and according to the law of
Lenz, the current generated is always such as to oppose the motion of
the closed circuit.
All magneto-electric and dynamo-electric machines are based on the
principle stated above, and are subject to many modifications.
The name _dynamo_-electric machine is given to it, because the electric
current is not induced by a _permanent magnet_, but is accumulated by
the mutual action of electro-magnets and a revolving wire cylinder or
armature. It is found that, as the dynamic force required to drive the
machine increases, so also does the electric current; it is therefore
called a dynamo-electric machine.
_Description._--In the machine here described, of which Fig.
164 is an elevation, Fig. 173 a part elevation, and Fig. 165 a
longitudinal section, the electric current is produced by the rotation
of an insulated conductor of copper wire or armature coiled in
several lengths, 8, 12, 16, &c., up to 28, and in several layers,
longitudinally, upon a cylinder with a stationary iron core _nn' ss'_,
so that the whole surface of the armature is covered with longitudinal
wires and closed at both ends, as in Fig. 165. This revolving armature
is enclosed to the extent of two-thirds of its cylindrical surface by
curved soft iron bars _NN__{1}, _SS__{1}.
[Illustration: Fig. 164.]
The curved bars are the prolongations of the cores of the
electro-magnets _E E E E_. They are held firmly together by screws to
the sides or bottom of the cast iron frame of the machine, making it
compact and strong.
The coils of the electro-magnet form with the wires of the revolving
armature one continuous electric circuit, and, when the armature is
caused to rotate, an electric current (which at first is very feeble)
is induced by the remanent magnetism in the soft iron bars and directed
through the collecting brushes into the electro-magnet coils, thus
strengthening the magnetism of the iron bars,[V] which again induce a
still more powerful current in the revolving armature.
The electric current thus becomes stronger and stronger, and the
armature therefore revolves in a magnetic field of the highest
intensity, the limit of which is governed by the limit of saturation of
the soft iron.
At each revolution the maximum magnetic effect upon each convolution
of the armature is produced just after it passes through the middle of
both magnetic fields, which are in a vertical plane passing through the
axis of the machine (i. e. _N__{1}_S__{1} in Fig. 173). The minimum
effect is produced when in a plane at right angles to it, i. e.
horizontal.
[Illustration: Fig. 165.]
According to the law of Lenz already referred to, when a circuit starts
from a neutral position on one side of an axis towards the pole of a
magnet, it has a direct current induced in it, and the other part of
the circuit which approaches the opposite pole of the magnet has an
inverse current induced in it; these two induced currents are, however,
in the same direction as regards circuit. A similar current will also
be induced in all the convolutions of wire in succession as they
approach the poles of the magnets.
These currents, almost as soon as they are induced, are collected by
terminal rollers or brushes _B_, usually the latter, placed in contact
with the commutator in the position which gives the strongest current.
The position giving the strongest current gives also the least spark,
so that when there are no sparks at the commutator the best lighting
effect is produced. Fig. 166 shows position of brushes when the
armature revolves in the direction indicated by the arrow.
The circumference of the revolving armature is divided into an
even number of equal parts, each opposite pair being filled with
convolutions of insulated wire wound parallel to the axis of the
armature.
The ends of these wires are brought to a commutator and connected to
the segments either by screws or by soldering.
The brushes collect the electric currents as they are induced, which is
nearly constant and continuous.
The collecting brushes are combs of copper wire placed tangentially to
the cylindrical commutator, and press lightly upon it with an elastic
pressure.
[Illustration: Fig. 166.]
_Power and Light produced._--An increase of the armature speed produces
a corresponding increase in the current produced, but not in the same
proportion. The current increases more rapidly than the speed, and
could be made to reach any intensity but for considerations explained
below. With increase of current there is also increase of heat.
The speed for continuous work must not be taken too high, because the
heat developed at high velocities might destroy the insulation of the
coils of the electro-magnet. The speed given for this machine produces
no such injurious heating effect.
The strength of the current is also influenced by the resistance of the
electric lamp and its leading wires. With an electric lamp in a circuit
of proper resistance the armature should revolve at the rate given in
the following Table. The heating will then reach its maximum, which
is very moderate, in about three hours after which there will be no
further change.
------------------------------------------------------------------
TABLE.
-------+---------------------+---------------------+--------------
Size. |Number of revolutions|Intensity of light in|HP (actual) to
| of armature. | standard candles. | drive.
-------+---------------------+---------------------+--------------
Medium | 800 to 850 | 4,000 to 6,000 | 3-1/2 to 4
-------+---------------------+---------------------+--------------
The intensity of the unassisted light is given in standard candles. The
standard here used is a stearine candle consuming 10 grammes per hour.
_Regulation._--From the fact that a closed circuit rotating in a
magnetic field experiences resistance to its motion which a broken
circuit does not, motive power to any extent is only required when
the circuit is closed. An interruption of the current is therefore
equivalent to removing the load from the motor, which for mechanical
reasons may be injurious to it and for electrical reasons to the dynamo
machine.
The sudden interruption of the circuit of the large machine produces
an electric tension so dangerously high as to strain or destroy the
insulation of the machine. When contact is again made after such
interruption, the increase of speed resulting from the interruption
causes a momentary current of great intensity, accompanied by sparks at
the commutator.
In order that the light may be quite steady the speed should be as
uniform as possible. As too high an increase of speed may result in
temporary extinction of the light, it ought never to be permitted. The
motor should therefore be provided with a good and sensitive governor,
that will keep the speed perfectly uniform however the steam and load
may vary. A large and heavy fly-wheel is also very useful in keeping
the speed nearly uniform during change of load.
Although the circuit, when the machine is in full action, should never
be suddenly interrupted, interruption arising from the extinction
of the light is _not_ dangerous, because it is always preceded by a
decrease in the strength of the current. When it is desired to divert
the current into another circuit it is advisable to stop the machine.
Although in practice with small machines this is rarely done, with
large machines it is necessary.
_Self-acting Shunt._--For great security, especially with the two
machines coupled together, where the electric current is strong and
the light equivalent to about 14,000 candles, it is advisable to insert
in the circuit a self-acting shunt.
[Illustration: Fig. 167.]
This is placed between the lamp and machine and connected to both
leading wires. Its principle is as follows:--
The terminal _M_, Fig. 167, is joined by a short connecting wire to
one terminal of the machine. The terminal _L M_ is connected to the
remaining terminal of the machine and also to one of the lamp terminals.
The terminal _L_ is connected to the other terminal of the lamp.
The shunt contains a small electro-magnet _E_ mounted upon a square
wooden slab or baseboard with its armature a, a contact c, and, below
the slab, a resistance coil _W_, which is equal to the resistance of
the electric arc of the light, about 1 S. _u._[W]
As long as the lamp is burning well, the current circulates in the
coils of the electro-magnet, and the armature _a_ being strongly
attracted, there is no contact at _c_. The resistance coil _W_ is
therefore not in electrical circuit. When the light is extinguished the
current in the coils of the electro-magnet ceases, and the armature is
withdrawn by the spring _f_ making contact at _c_. This offers to the
electric current a path through _W_ of equal resistance to that of the
lamp, and the current is subjected to scarcely any change, so that the
motor has practically no cause to alter its rate.
When the carbon points of the lamp again touch, the electric current
returns to them, breaking contact at _c_, re-establishing the former
conditions.
_Direction of Rotation._--The armature may revolve in either direction.
If it becomes necessary to drive it in the opposite direction to that
for which the machine has been made, it is only necessary to reverse
the brushes, placing their points in the direction of motion, and to
change two of the wire connections, which operations can be effected in
a few minutes. Fig. 166 shows the position of brushes for one direction
of rotation and Fig. 168 that for the other.
[Illustration: Fig. 168.]
_Conducting or Leading Wires._--The leading wires are usually of copper
of high electrical conductivity. They must be insulated from one
another the whole of their length and not placed too close together.
As their resistance affects the intensity of the light very much, the
section must be carefully proportioned to the distance of the lamp from
the machine.
The best practical result is obtained when their resistance together
with that of the lamp is equal to the total internal resistance of the
dynamo machine. Wires of various sizes are therefore required.
Decrease in strength of the current caused by a leading wire of too
high resistance can be overcome by a higher velocity, which is obtained
only by increased motive power, but if the wire is much too small, it
will become heated. The proper remedy is to increase the sectional area
of the leading wire.
Bright sparks should never be allowed to appear at the commutator and
brushes, as sparks result from a rapid burning of the metallic parts.
They can easily be avoided by properly inclining the two arms which
carry the brushes.
The position of the brushes yielding the least spark at the commutator
is that giving the highest intensity of light in the electric arc.
The commutator should, while in motion, be freely oiled, to prevent the
brushes wearing away too rapidly. The sticky oil should from time to
time be removed by washing with paraffine oil or benzoline.
_Wear and Tear._--The chances of stoppage so common to the old forms of
electric light apparatus have in this form been reduced to a minimum,
and now do not exceed those that arise with machines generally. The
Trinity House Report states that the Siemens' machine worked well for
a month without any necessity for stopping. The brushes are the only
parts which wear away, and they are very easily replaced.
In thick weather they should be connected in what is called parallel
circuit (or parallel arc, or for "quantity"), because it has been
found that when they are so arranged the intensity of the electric
light produced exceeds by some twenty per cent. the intensity of the
sum of the two when worked separately. Thus the two machines, giving
respectively a candle power of 4,446 and 6,563 when worked separately
(total 11,009), have given when coupled up in parallel circuit a light
equivalent to 13,179 candles; just as in telegraphy it has been found
that the rate of sending can be increased from 20 to 25 per cent. when
the apparatus is coupled up in parallel arc. For this reason it is
usual to employ two machines of medium size instead of one machine of
large size. The intense light so produced is also much more uniform
than from one large machine.
_Automatic Electric Lamp._--Automatic electric lamps have been
constructed with spring clockwork to cause the carbons to approach one
another to a certain point, when, by means of an electro-magnet, the
clockwork is checked, and the carbon points are allowed to burn away
to such a distance that, by the decrease of current, the clockwork is
released and the carbons caused to approach again. With such lamps the
clockwork has been a source of trouble, and it is liable to get out of
order.
_Siemens' Patent Electric Lamp._--The lamp here described is actuated
without clockwork; it also automatically separates the carbons after
they have approached too closely or touch, and, by this combined action
of approaching and separating, the carbon points are kept at a proper
distance apart, and a steady light is obtained.
The working parts are represented in the diagram Fig. 169, and at Fig.
170 is shown the size employed on board ship.
_E_ is the horse-shoe magnet with the armature _A_ placed in front of
its poles a short distance from them. A regulating screw _b_ with the
spiral spring _f_ is attached to the lever _A'_, forcing it against
the stop _d_, and withdrawing the armature from the poles of the
electro-magnet. When a current traverses the coils of the latter of
sufficient strength to attract the armature and overcome the tension
of the spring _f_, contact is made at _c_, which diverts the current
from those coils. The consequent release of the armature breaks contact
at _c_, the armature is again attracted, and this action is repeated,
producing a vibrating motion of the lever and armature, which continues
as long as there is sufficient current to overcome the tension of the
spring.
[Illustration: Fig. 169.]
The spring pawl _s_ at the upper end of the lever _A'_, and oscillating
with it, actuates a ratchet-wheel _u_, which is in gear with a train
of wheels and the carbon holders; it thus opposes their tendency to
approach by pushing them apart, tooth by tooth, until the current is
so much weakened by the increased length of electric arc that the
armature and lever cease to oscillate enough to move the teeth of the
ratchet-wheel, and it rests near the stop _d_.
While in this position the spring pawl is released from the
ratchet-wheel and the preponderating weight of the upper carbon holder
causes the carbon points to approach again. Increase of current follows
decrease of resistance, the armature again oscillates, and this cycle
of action is continuously repeated.
When in action the movements of the carbons are scarcely perceptible,
but when, by any external cause, the carbons are separated so as to
extinguish the light, they immediately run together until they touch,
when they ignite and separate to a proper working distance by means of
the electro-magnet above described.
The only operation requiring attention in the use of this lamp is the
adjustment of the tension of the spring _f_. When this tension is once
regulated to the current at disposal, the lamp will continue to give a
steady light as long as the current remains uniform.
The relative rate of consumption of the two carbon points differs. The
positive carbon burns away rather more than twice as quickly as the
negative carbon.
[Illustration: Fig. 170.]
The duration of the light depends mainly on the lengths and sizes of
the carbons.
Provision is made in this lamp that the rack which supports the
negative carbon may be made to gear either into the teeth of the same
pinion as that of the positive carbon, or into one of about half the
size. By these means the light, when once focussed in a reflector,
will remain in focus as long as the carbons last, whether permanent or
reversed currents are employed.
Besides its twofold application, the lamp is very compact, is simple in
construction, and therefore not likely to get out of order, and it is
capable of being regulated with great precision.
There is no spring to be wound up. The contact need not be cleaned, as
the sparks are scarcely perceptible.
By removing two screws in the outside casing, all the chief working
parts can be easily removed and inspected.
Carbons are made from the hard carbon deposited in the interior of
gas retorts, also from graphite. Various sizes, both square and round
in section, of from 5 to 20 mm. in diameter, are used in the electric
lamp according to the intensity of the electric current. Those commonly
employed are from 10 to 12 mm. in diameter.
The carbons supplied with the Siemens patent lamp are coated with a
thin film of copper. This enhances the cost somewhat, but it greatly
improves the result, as the carbons burn longer, and do not split, when
so coated.
By coating them the resistance is diminished, except at the points, so
that all the heat is concentrated in the electric arc, and a brighter
light is the result.
When two dynamo machines are coupled together (see page 248), to give a
very powerful current, the sizes up to 20 mm. are required.
The consumption varies a little, but the average is from 3 to 4 inches
per hour.
[Illustration: Fig. 171.]
_Concentration of Light._--Two kinds of concentrating apparatus are
supplied in combination with the automatic lamp, both of which are
capable of giving a powerful parallel beam, which will reach to an
enormous distance, and are well adapted for naval purposes. The one
kind consists of a parabolic reflector of stout metal, its concave
surface being silvered and burnished. The apparatus is mounted with a
ball-and-socket joint upon a wooden stand, as shown in Fig. 171.
The other kind is the Fresnel catadioptric lens or holophote, Fig. 172,
which may be substituted for the reflector, and gives a more powerful
beam than one given by reflection. The lens is surrounded by a metal
case or lantern, in which is placed the electric lamp upon a slide
for focussing. Behind the carbon points a hemispherical reflector is
placed, to catch all the back rays, and reflect them back through the
lamp focus. The entire lantern is capable of revolving on horizontal
rollers, and swings upon pivots. Two handles are placed at the back to
manipulate it.
[Illustration: Fig. 172.]
As the electric arc is much too bright to be looked into with the naked
eye, both concentrating apparatus are supplied with a lens, called a
focus or flame observer, by means of which an image of the burning
carbons is thrown upon small screens at the back, so that the lamp can
be easily adjusted without fatigue to the eye. The focus observer is
shown on the lamp in holophote, Fig. 172.
_Precautions._--Before starting the apparatus, the electric lamp
terminals and those of the dynamo machine must be _connected up_ by
means of the leading wires provided with each set of apparatus. The
terminals are marked _C_ and _Z_ respectively, and they should be
connected, _C_ of machine to _C_ of the lamp, and _Z_ of the machine to
_Z_ of the lamp, in order that the electric current may be sent in the
proper direction through the carbons of the lamp. Should it, however,
be found that the top carbon (which should consume twice as fast as
that of the bottom one) does not consume so fast as the bottom one, it
may be assumed that the dynamo machine has reversed its poles, and the
leading wires will consequently require changing across. This reversal
of poles, though possible, is of _very rare_ occurrence.
[Illustration: Fig. 173.]
The dynamo-electric machine should not be driven without its proper
leading wires to lamp and lamp being connected up, or at least
an external resistance equivalent to that of the lamp (which is
approximately one Siemens' unit) must be inserted. In other words, the
machine must not be driven when a wire of small resistance connects the
two terminals _C_ and _Z_. This is expressed more briefly by saying the
machine must not be _short-circuited_. If it is short-circuited when
in motion the electric current becomes so powerful that it will leap
from segment to segment of the commutator, where very bright and large
sparks will be seen, and if continued would destroy the insulation,
thus weakening the current generated.
The leading wires should never be disconnected suddenly while the
machine is revolving at its full speed, as such a sudden interruption
will produce an intense spark, which will burn the ends of the wire
where the contact is suddenly broken. When it becomes necessary to
disconnect the wires, the belt should be pushed on to the loose pulley
by means of the striking gear, or the steam engine should be stopped.
It may be here stated that all connections should be cleaned bright and
screwed tightly, to ensure perfect metallic contacts being made.
_Coupling two Machines._--At Fig. 174 is shown a diagram of how to make
the connections when coupling two machines in parallel circuit. _MM'_,
_m_, _m'_, represent the ends of the wires of the electro-magnets;
_BB'_ are the branches; _C_ and _Z_ are the terminals of each machine
respectively.
[Illustration: Fig. 174.]
The three ways in which the various wire connections of these machines
are joined up, and which are enough for all ordinary purposes, are
given below in paragraphs (_a_), (_b_), and (_c_).
(_a_) When the machine is working _singly_ and revolving in the
direction indicated in Fig. 166, the following connections are made:--
_M_ is connected with _B_,
_M'_ " _B'_,
_m_ " _Z_,
_m'_ " _C_,
and the leading wires of the lamp are connected with _C_ and with _Z_
as explained.
(_b_) When working _singly_ and revolving in the direction indicated in
Fig. 168:--
_M_ is connected to _B'_,
_M'_ " _B_,
_m_ " _Z_,
_m'_ " _C_.
Thus the only change necessary when the machine is to be driven in the
opposite direction to that for which it is made, is to disconnect at
_B_ the wire from _M_ to _B_ and at _B'_ the wire from _M'_ to _B'_,
and to cross them. The machine will then be connected as above (_b_).
(_c_) When working _two_ machines in parallel circuit, as in Fig. 174,
they must be connected as follows (that on the left of the page being
called the first machine, and that on the right the second machine):--
_C_ of first to _C_ of the second.
_Z_ " _Z_ "
_M_ " _B_ "
_B_ " _M_ "
_M'_ " _B'_ "
_B'_ " _M'_ "
and then connect _C_ and _Z_ of the second machine with the leading
wires of the lamp.
The connections _m_ to _Z_ and _m'_ to _C_ in each machine are the same
as in cases (_a_) and (_b_). They do not require to be altered, and may
therefore be left out of consideration in all three cases (_a_), (_b_),
and (_c_). The whole of the connections here indicated can be quickly
made by means of a cross-bar commutator or switch, which is supplied
with the machines in cases where such changes are likely to be required
frequently. This is usually attached to a wall, leading wires being
taken to it from the dynamo machines separately, and others from the
switch being led to the electric lamps.
The leading wires from machine to lamp should, whenever possible, be
kept _separate_, to prevent them rubbing together and making contact. A
distance of two inches is quite sufficient to prevent accidents of any
kind.
When the leading wires are erected in places where they are likely to
rub and chafe against hard substances, it is advisable to enclose each
wire separately in india-rubber tubing at all the points where they are
likely to be rubbed. This becomes very important on board ship, where
everything is in motion, and special care is in consequence required.
Some dynamo machines are coupled direct to the crank shaft of the steam
engines; they require the same kind of attention as others, that is to
say, they should be driven at a uniform speed, should be well oiled as
well as the steam-engine, and they should be kept clean and free from
sharp grit.
_Application._--The electric light used in the case of a _direct_
attack by torpedo boats, without the assistance of guard boats, will
not prove of much assistance, on account of the very small space
covered by the beam of light, and therefore if the direction of attack
is not exactly known, the beam of light must be kept continually
sweeping round the horizon on the chance of picking out the attacking
boats, and thus, while flashing in one direction, they may be
approaching in another, and effect their deadly mission.
Every man-of-war should be fitted with at least three electric lights,
whereby the above-mentioned want of space covered would be to a
considerable degree obviated.
If a powerful beam of light be thrown in a particular direction, and
there kept stationary, all boats or vessels crossing its path at a
distance not exceeding 1600 yards from the ship using the electric
light, would become distinctly visible to observers placed behind the
light; these vessels remaining visible as long as they continue in such
a position that the beam of light acts as a background to them. Under
very favourable circumstances, the distance at which the above effect
may be observed is much increased.
The parabolic reflector extends only about an arc of 33° at 540 yards'
distance from the light.
One defect of this form of reflector is, that it is rapidly dimmed by
spray, rain, and by the particles given off by the carbons.
The catadioptric lens, or holophote, gives a far more powerful but a
more concentrated beam than the parabolic reflector. By means of such
a beam of light, a torpedo boat may be discerned at about one mile
distance. By adding divergent lens to the holophote, a less powerful
and less concentrated beam of light will be thrown out; in this case
about 20° of surrounding water would be well illuminated at about 900
yards' distance, while without the divergent lens there would be only
about 5° so illuminated but far more brilliantly.
The distance at which objects can be detected by the electric light
depends on their size and _colour_, more particularly on the latter.
The observer should as a rule be well removed from the light.
In the case of an electric light being thrown on the observer, the
vessel, &c., using it would to that observer be invisible, the
light only being seen; also when directed on any particular object,
surrounding objects would be thrown into shade.
The electric light will be found very useful for signal purposes by
fitting a plane mirror in front of the catadioptric lens; so arranged
that it be turned to any desired angle to the axis of the beam of
light. By altering the angle of the mirror, the reflected beam of
light can be swept from the horizon on one side, through the zenith,
to the horizon on the other side. The time of passing the zenith being
equivalent to the long and short flashes of the usual night signal code.
In addition to using the electric light to detect the approach of
torpedo boats, it may be used by the boats themselves to prevent the
attacked vessel from discerning them.
In turret ships, electric lights may be so arranged that the instant an
object is brought into the field of the beam of light, the turret guns
will be bearing on it.
One great disadvantage of electric lights is the impossibility of
protecting them from the enemy's fire, and this is a defect that cannot
be eradicated, though it may be lessened, by manipulating them from the
tops of a ship.
_Torpedo Guns._--Hitherto by torpedo guns has been meant small guns
mounted on carriages so constructed that a shot may be fired into
the water only a few feet from the ship's side, or mitrailleuses,
Gatlings, &c. Here the term is applied only to machine guns, which are
constructed to fire either volleys, or, extremely rapidly, single shot,
each shot of which would be capable of _penetrating_ and _sinking_
torpedo boats, such as Messrs. Yarrow and Thornycroft are daily
launching from their yards. Of such weapons there are at present only
two, viz., the "Nordenfelt" and "Hotchkiss" gun. The former has, after
very exhaustive experiments, been adopted by the English, Austrian,
Swedish, and other naval authorities, while the latter has been adopted
by the French government.
_Nordenfelt Torpedo Gun._--This gun, as it at present is constructed,
consists of four barrels of 1 inch calibre.
The barrels are fixed in a horizontal plane, and are not moved during
the firing; and the movement of the lever, the loading, the firing,
and the extracting are all performed in the same plane, so that the
_elevation_ of the gun is not disturbed by the firing.
The gun is fed by means of hoppers, each of which contains ten rounds
per barrel, _i. e._, forty shots.
The continuous supply of cartridges, as well as the firing and
extracting, are all performed by one motion of the lever, thus enabling
the gunner to use his left hand to lay the gun.
A volley of four shots can be fired at the same moment, or one shot can
be fired separately. Eight shots can be fired in 1-1/4 seconds; twenty,
thirty, or forty shots can be fired at a rapidity of two hundred shots
per minute without difficulty.
The recoil being taken up by the whole framework of the gun does not in
the least disturb the aim.
The entire mechanism of the gun can be opened up without undoing a
single screw, in less than 20 seconds.
All the four spiral firing springs can be taken out, without opening
the rest of the mechanism, in 1-1/2 seconds.
All the parts of the mechanism are made interchangeable, so that
reserved parts can at any time be substituted. The gun can be placed on
half cock, so that the strikers do not act; and for further security
the lever can be locked. The carrier block, without which the gun
cannot be fired, is loose, and can be taken away, in case it becomes
necessary to abandon a gun, which is thus made useless to the enemy.
The bullets are solid steel, weighing about 1/2 lb. At 1760 yards at
right angles this gun will penetrate a 3/16 inch steel plate, which
represents the thickness of the plates of a torpedo boat.
At 200 yards at right angles it will penetrate one 3/16 inch steel
plate placed in front of a 1/2 inch steel plate with a space of 3 feet
between them, this target representing the plates and boiler of a
torpedo boat.
At the same distance, at 30° angle against the line of fire, it will
penetrate a 1/2", 1/4", or 3/16" steel plate.
The holes in some instances are from 6 to 11 inches in length, and
2-1/2 inches in height. Angle of depression 20°, of elevation 30°, and
of direction 360°.
Weight of the gun 3-3/4 cwt., and weight of carriage 2-1/2 cwt.
_Hotchkiss Torpedo Gun._--This gun consists of a group of five barrels,
revolving on a central shaft, a breech block, containing the firing
mechanism, a feeding hopper, and the necessary hand crank for training
and firing. The gun is mounted on trunnions attached to a vertical
column, which rests in a suitable socket bolted to the ship's side; by
this means a universal motion is obtained.
The essential difference between this and the Nordenfelt gun is, that
the _barrels_ and mechanism are put into rotatory motion.
Another point of difference is that single shots only can be fired, and
not a volley, as in the Nordenfelt gun.
With the Hotchkiss gun, only some thirty shots can be fired in one
minute at an advancing torpedo boat. The weight of the Hotchkiss steel
shot is about 1 lb., but owing to the low velocity of the gun, its
penetrative power is little more than that of the Nordenfelt 1/2 lb.
bullet.
The object to be gained in firing at an attacking torpedo boat is to
sink her, and not merely to kill or disable her crew, for supposing the
attack to be made with a contact spar torpedo, and the boat to have
reached within 300 yards' distance from the ship, then, even if all
the crew (probably two or three men) were disabled or killed, the boat
would, if not sunk, still carry out its work of destruction; therefore
the projectiles to be used under such circumstances should be only
those capable of penetrating a torpedo boat's plates, _i. e._, solid
steel shot, not shells.
_Diving._--In laying down and in picking up submarine mines, divers
will be found extremely useful; also in clearing a passage in a
river, &c., of an enemy's torpedoes in time of war. During the late
Turco-Russian war, the harbour of Soukoum Kaleh taken by the Turks was
_popularly_ supposed to have been cleared of its mines by native divers
(Lazees), but as the torpedoes so captured were never seen at Stamboul,
it must have been a stretch of imagination; probably such would have
been done, had there been any mines in the harbour to clear away.
The following is a general description of Messrs. Siebe and Gorman's
improved diving apparatus.
The apparatus consists of
1. An air-pump.
2. The diving dress.
3. The breast-plate.
4. The helmet.
5. The boots.
6. The crinoline.
_Air-pump._--This improved air-pump consists of two double action
cylinders, each cylinder capable of supplying about 135 cubic inches
per revolution. The advantage of this air-pump is, that it can supply
air to two divers, working independently and at different levels,
each diver being in direct connection with one of the cylinders. The
air-pipes are in lengths of 45 feet and 30 feet, made of vulcanised
india-rubber with a galvanised iron wire imbedded; this protects from
corrosion, and allows the air to pass through the pipes with less
friction.
_Diving Dress._--The diving dress is made of solid sheet india-rubber,
covered on both sides with tanned twill; it has a double collar, the
inner one to pull up round the neck, and the outer one of vulcanised
india-rubber to go over the breast-plate and form a water-tight joint.
The cuffs are also of vulcanised india-rubber, and fit tightly round
the wrist, making, when secured by the vulcanised india-rubber rings, a
water-tight joint, at the same time leaving the diver's hand free.
_Breast-plate._--The breast-plate is made of tinned copper, and has a
valve in front, by which the diver can regulate the pressure of air
inside his dress and helmet. The outer edge of the breast-plate is of
brass, and is secured by screws to the outer collar of the dress.
_Helmet._--The helmet is made of tinned copper, and has a segment
bayonet screw at the neck, corresponding to that of the breast-plate,
which enables the helmet to be removed from the breast-plate by
one-eighth of a turn. It has three strong plate glasses in brass
frames, protected by guards; two oval at sides, and a round one on the
front; the front one can be unscrewed, to enable the diver to give
and take orders. At the side is an outlet valve, which, by inserting
a finger, the diver can close, and so rise to the surface. The valve
allows the foul air to escape, and prevents the entrance of the water.
An elbow tube is securely fitted on the helmet, to which is fixed an
inlet valve, to which the air-pipe is attached. The inlet valve is
made that the air can enter, but in case of a break in the air-pipe it
cannot escape.
The front and back weights are of lead, heart-shaped, and weigh about
40 lbs. each.
_Boots._--The boots are made of stout leather, with leaden soles, and
are secured over the instep by a couple of buckles and straps. Each
boot should weigh at least 20 lbs.
_Crinoline._--The crinoline or shackle is used for deep water; it is
placed round the body and tied in the front of the stomach: being
supported by braces, it affords protection to the stomach, and enables
the diver to breathe more freely.
_Ladder._--An iron ladder should be provided with stays to bear against
the side of the boat from which the diving is carried on, to which may
be attached (if working in deep water) an ordinary rope ladder, with
ash rounds, and weighted at the end. Some divers have the ladder only
20 feet long, to the last round a rope with a weight attached, which
rests on the ground; by that means they descend.
_Directions for using the Apparatus._--The ladder having been fixed,
the position of the pump should be decided on, and it should be
securely lashed by means of the ropes attached to the handles down to a
stage, into which the _screw-eyes_ should be fastened if necessary; the
pump should be placed out of the way of the divers, the men attending
on them, and all the men employed. The best position for the pump is
facing the head of the ladder, and about six feet from it.
While the diver is dressing, the pump should be prepared for use,
the winch handles should be taken out of the pump case, the nipples
protecting the crank axles removed, the nuts being replaced on their
screws. The nuts for the ends of the crank axles are taken off, the
fly-wheel placed on the shaft, and the winch handles put on, and
secured by the nuts, which are screwed home with the spanner. The pump
is always worked in its case.
The flaps covering the pressure gauges and that at the back of the
pump case should be opened, the screw on the overflowing nozzle of the
cistern removed, and the cistern filled with water; the caps of the air
delivery pipes should be removed, the necessary lengths of air-pipe
should be put together carefully with washers in place, and all the
screws must be worked home by means of the _two_ double-ended spanners.
The air-pipes should be tested by holding the palm of the hand to the
end of the pipe, till the pressure shown on the pressure gauge is
considerably above that corresponding to the depth the diver is to
descend.
_Dressing the Diver--Crinoline only for Deep Water._--The diver having
taken off his own clothes, puts on a guernsey, a pair of drawers,
very carefully adjusted outside the guernsey, and securely fastened
by the tape round the waist, to prevent them from slipping down, and
then a pair of inside stockings. If the water be cold, the diver may
put on two or more of each of the above articles. He then puts on the
crinoline and woollen cap, drawing the latter well over his ears; some
divers find relief from putting cotton saturated with oil in their ears.
The _shoulder pad_ is then put on, and tied under the diver's arms.
He then gets into the diving-dress, which in cold weather should be
slightly warmed, drawing it well up to his waist; he next puts his arms
into the sleeves, an assistant opening the cuffs by means of the cuff
expanders, or by inserting the first and second fingers of both hands,
taking care to keep his fingers straight. The diver, by pushing, forces
his hand through the cuff. He puts on a pair of outside stockings and a
canvas overall to preserve the dress from injury.
The diver then sits down, and the inner collar of the dress is drawn
well up and tied round the neck with a piece of spun yarn, and the
breast-plate put on, great care being taken that the india-rubber of
the outer collar is not torn in putting it over the projecting screws
of the breast-plate. The four pieces of the breast-plate band, which
with the thumbscrews had been previously placed for safety in one of
the boots, are then put over the outer collar, and secured to the
projecting screws by means of the thumbscrews; the centre screw of each
plate should be tightened first. It will generally be sufficient if the
thumbscrews be screwed up hand-tight, the spanner being only used when
necessary. The canvas overall is now adjusted and the boots are put on.
The rings are passed over the cuffs, and the sleeves of the overall are
drawn down to cover them. If gloves are to be used, the rings will be
put on over them, as well as the cuffs. The helmet (without the front
bull's-eye) is then put on; before doing so, the attendant should blow
through the outlet valve of the helmet; he can do so by placing his
head in the interior, and placing his mouth to the hole where the air
escapes. Blow strongly; if in proper working order, the valve will
vibrate. A loop of the life line is placed round the diver's waist, the
line brought up in front of the man's body, and secured with a piece of
small rope passing round his neck, or to the stud on the helmet. The
waist-belt is buckled on with the knife on the left side, the end of
the air-pipe being passed from the front, through the ring on the belt
on the man's left, and up to the inlet valve on the helmet, to which it
is secured; the upper part of the pipe is then made fast by a lashing
to the stud on the left of the helmet. The diver then steps on the
ladder, and two men are told off to _man the pump_.
The weights are then put on, the front weight first, the clips being
placed over the studs on the breast-plate. The back weights are then
put on, and the clip lashings over the hooks on the helmet, and the two
are secured to the diver's body by means of the lashing from the back
weight, which is passed round the waist, through the thimble beneath
the front weight, and tied to the other end of the lashing at the back
weight.
When the signalman is sure that all is right, and that the diver
understands all the signals, he gives the word _Pump_, and screws the
centre bull's-eye into the helmet securely; this done, he takes hold of
the life line and "pats" the top of the helmet, which is the signal for
the diver to descend.
_Signals employed._--The signalman is the responsible person, and must
be very vigilant all the time the diver is down; occasionally he will
give one pull on the life line, and the diver should return the signal
by one pull signifying "all right;" if the signal be not returned, the
diver must be hauled up, but if the diver wishes to work without being
interrupted by signal, he gives one pull on the line, independently,
for "All right; let me alone." If the signalman feels any irregular
jerks, such as might be occasioned by the diver falling into a hole, he
should signal to know if he is all right, and if he does not receive
any reply, he should haul him up immediately. If the diver from any
cause is unable to ascend the ladder, and wishes to be pulled up, he
gives four sharp pulls on the life line. If while being hauled up the
diver gives one pull, it signifies "All right; don't haul me any more."
The diver should be hauled up slowly and steadily. If the signalman
wishes the diver to come to the surface, he gives four sharp pulls on
the line, on which the diver should answer "All right," return to the
foot of the ladder, and signal to be hauled up.
_One_ pull on the air-pipe signifies that the diver wants more air.
_Two_ pulls on the life line and _two_ pulls on the air-pipe in rapid
succession, signify that the diver is foul and cannot release himself,
and requires the help of another diver; on receiving such a signal, no
attempt should be made to haul the diver to the surface.
The above signals are to be invariably used; but other signals may be
arranged as is most convenient for any particular work, as a great
variety can be made with the life line and air-pipe. The diver can
communicate with the surface by means of a slate.
Further information on this subject, especially with regard to the
foregoing diving apparatus, will be found in Messrs. Siebe and Gorman's
"Manual for Divers."
FOOTNOTES:
[Footnote V: In wrought iron there is always some residual magnetism;
there is therefore no necessity to start the magnetism with a permanent
magnet.]
[Footnote W: Siemens' unit.]