DEFENSIVE TORPEDO WARFARE--_continued_.
_CLOSING the Electric Circuit._--In connection with the system of
coast defence by means of electrical submarine mines, there are two
distinct methods of effecting the closing of the electric circuit, and
consequently, the firing battery being connected, the explosion of the
mine or mines, which methods may be used separately, or in combination,
and are as follows:--
1.--The self-acting method.
2.--The firing by judgment, or observation method.
During the early days of submarine defensive warfare, the latter method
alone was used, owing to the absence of anything like a practicable
form of self-acting apparatus; but within the last few years, the
former has almost entirely superseded the latter method, except in very
exceptional cases; this revolution being due to the vast improvements
that have been, and still are being effected in the system of firing
electrical submarine mines automatically.
_Use of Circuit Closers._--Electrical submarine mines may by means of
an apparatus, termed a _circuit closer_, be rendered self-acting; that
is to say, by the action of a vessel coming in contact with such an
apparatus, which may be either within the mine itself, or within a buoy
attached to the mine, the electric circuit is closed, and the mine in
connection with the circuit closer so struck, exploded. The essential
feature of such a mode of closing the electric circuit is, that
electrical submarine mines may be rendered either active or harmless,
at the will of the operator, which is effected by the putting in, or
taking out of a plug, by which means the firing current is either
thrown in, or out of the circuit.
_Circuit closers._--Many different forms of circuit closers have been
devised, among which the following seem the most suitable and are those
generally used:--
1.--Mathieson's inertia circuit closer.
2.--Mathieson's spiral spring circuit closer.
3.--Austrian self-acting circuit closer.
4.--McEvoy's mercury circuit closer.
5.--McEvoy's weight magneto circuit closer.
_Mathieson's Circuit Closer._--This form of circuit closer has been
adopted by the English government in connection with their system of
defence by electrical submarine mines.
The details of this apparatus are shown at Pl. xiii.
Fig. 53, _a_ is a gun-metal dome screwed on to a metal base _b_, its
foot resting on a gutta percha washer _c_, so as to exclude any water;
_d_ is a cap screwed on to the top of the dome, and made watertight
by the leather washer _e_; _f_ is a guard cap screwed into the cap
_d_, this is to keep the spindle of the circuit closer steady during
transport, and would be removed when the apparatus is prepared for
service; _g_ is the ebonite base plug through which pass the insulated
wires _E_ and _L_; _h_ is an hexagonal collar, working in the metal
base plate _b_, by means of which, and the brass collar _i_, and the
leather washer _k_, the base plug is secured, and water is excluded
from the interior of the circuit closer; _l_, _l_, _l_ are brass
columns supporting a circular ebonite piece _m_; _n_ is a metal bridge
screwed on to the base plate _b_, into which is screwed the spindle
_p_, both of which are prevented from moving after being screwed up by
the set screws _r_ and _s_.
The spindle _p_ carries a leaden ball _t_, which is supported upon the
rest _v_, and is secured in position by the screw nut _w_; _x_ is an
india rubber ring, the object of which is to prevent any damage being
done to the spindle should the ball when set in action by a heavy
blow from a passing vessel be brought into contact with the dome; 2
is a brass disc attached to the spindle carrying an ebonite disc 4,
connected to it by screws; 6 is a brass contact ring also fixed to the
ebonite disc 4, provided with a screw 8, for the attachment of one of
the base plug wires, and with platinised projections 3, 3, 3, Fig.
56. The contact ring 6 is completely insulated from the spindle and
brass disc 2. Three contact springs 5, are attached to the circular
ebonite piece _m_, and the faces opposite to the platinised projections
of the disc 2 are also platinised. 7 shows the contact screws of the
connecting pieces, which serve also as adjusting screws to regulate the
sensitiveness of the apparatus, the points of which as well as their
bearings on the springs are platinised.
The springs are connected together by means of the wires 9, Fig. 55,
one end of which is secured to the connecting piece by the screw 10,
and the other passes through to the top of the ebonite piece, and is
attached to the top of the spring next in succession to that to which
it is fixed below.
One terminal of a coil of 1000 ohms resistance (which is used for
testing purposes) is attached to the line _L_, terminal of the
ebonite base plug, which latter is also connected to the screw 8, on
the circumference of the contact ring 6; the other terminal of the
resistance coil is connected to the earth, _E_ terminal of the base
plug.
A bare copper wire of No. 16 B. W. G. connects the top of the last
contact spring with the set screw _s_; a piece of similar wire jointed
to it is passed round one of the brass collars and connected to the
screw _r_. As a precaution against bad contact, the contact springs
are connected together by bare wires _A_, _B_, _C_. This completes the
connections for the signalling circuit, the earth being formed by the
body of the instrument; _D_ is a hole left in the metal base for the
passage of the insulating wire which connects the earth plate to the
earth _E_ terminal of the base plug.
_Testing Current._--For testing purposes the current from the test
battery arrives by the line wire _L_, and passes thence through the
resistance coil to earth by means of the wire _E_, which is attached
to a zinc earth plate placed in a recess in the jacket of the circuit
closer.
_Action of the Circuit._--The action of the apparatus is as follows:--
_Closer._--On the circuit closer being struck, the weight of the lead
ball _t_ causes the steel rod _p_ to be deflected and brings the brass
ring 6 in contact with one of the springs 5; the signalling current
which up to this moment has been passing through the 1000 ohms coil
to earth, then passes to the contact ring 6 (avoiding the resistance
coil) thence to the spring which is in contact with it, and from there
by means of the wire connections to the set screws _s_ and _r_, and so
to earth through the metal body of the apparatus; the effect of the
resistance coil being thus eliminated, is to strengthen the signalling
current, and thus enable it to work the shutter apparatus, by which
means the firing current is thrown into circuit and the mine exploded.
[Illustration: MATHIESON'S CIRCUIT CLOSER.
PLATE XIII]
_Circuit Breaker._--By altering the mode of connecting the wires, the
above apparatus may be used as a circuit breaker, that is to say, the
signal may be given, and the mine exploded by the cessation of a
passing current, instead of by the closing of the electric circuit.
This system was specially designed for use with platinum wire fuzes,
but is rarely used.
_Circuit Closer of Electro Contact Mines._--When the inertia circuit
closer is employed in connection with electro contact mines, the
circular ebonite piece _m_ is replaced by a similar shaped piece of
brass, and which is in metallic connection through the brass pillars
_l_, _l_, _l_ with the mass of the metal of the apparatus which forms
the earth plate.
The insulated wire of the base plug is connected to one pole of a
platinum wire fuze, the other pole of which is connected by another
wire to the outer metal rim of the disc of the spindle. As long as the
circuit closer remains undisturbed, a break will remain in the circuit,
which is due to the ebonite insulation between the spindle and the
outer metal rim of the disc; but the moment the apparatus is struck,
which causes the spindle to vibrate, the outer metal rim will come in
contact with one of the springs completing the circuit, through the
circular metal portion and the pillars of the circuit closer to earth.
_Adjustment of Circuit Closer._--The sensitiveness of Mathieson's
inertia circuit closer is determined by the distance between the
disc 4 and the springs 5, 5, 5, which is regulated by means of the
adjusting screws 7, 7, 7, which press against the inner faces of the
springs. Owing to the great weight of the leaden ball, when by any
cause the circuit closer is inclined for a length of time, a permanent
set is given to the spindle, thereby destroying the adjustment of the
instrument.
_Improvements in the Inertia Circuit Closer._--To remedy this very
serious defect, a cylinder of india rubber is substituted for the
leaden ball; a circuit closer so fitted is also less affected by the
action of counter mines, which is a very important advantage.
_Mathieson's Spiral Spring Circuit Closer._--A sectional elevation of
this form of circuit closer is shown at Fig. 57. It consists of a brass
base _a_, provided with a grooved flange for carrying a gutta percha
washer, and it has also an hexagonal projection for the purpose of
screwing the circuit closer into the gun-metal mouth of its air-tight
cylinder, or buoy; _b_ is a brass dome enclosing the apparatus for the
purpose of protecting it from injury, and also by means of india rubber
washers to prevent an ingress of water, should the circuit closer case
become injured, and leak; _c_ is a brass collar to which the brass
contact springs _i_, _i_ are attached, and which are regulated by the
set screws _j_, _j_; a brass spiral spring _d_ carries a metal rod _e_,
which supports a brass ball _f_, surrounded by an india rubber band
_h_. A contact disc _g_ is secured to the base of the spindle _e_, but
insulated from it by an ebonite boss; _k_ is an ebonite base plug with
two channels in it, through which the wires _m_, _m^{1}_ pass.
_An Improvement on the Inertia Circuit Closer._--This instrument is
a vast improvement on the inertia apparatus previously described,
being more simple and more certain in its action, a desideratum in
all circuit closers; but notwithstanding, up to the present time
Mathieson's inertia apparatus has been used by our government, to the
exclusion of all other instruments of a similar nature, some of which
were proved to be far superior when subjected to the crucial test of
actual practice.
_Austrian Self-acting Circuit Closer._--This form of circuit closing
apparatus, which is purely a self-acting one, that is to say, a mine so
fitted cannot be fired at will, is shown at Fig. 58.
It consists of several buffers _a_, _a_, _a_, which by means of
strong springs are held in position, their heads projecting outside
the torpedo case _b_; on being pressed in by the contact of a passing
vessel, the ends of these buffers would be forced against a ratchet
wheel _c_, which is also kept in position by means of a spring. Several
strong pieces of wood _d_, _d_ within the case keep the buffers and
their attached arms in the proper direction, and also afford rigidity
to the torpedo case. The brass ratchet wheel _c_ being put in motion
carries round with it a central arrangement _e_, the lower part of
which is shown at Fig. 58, _A_.
This portion consists of a cylinder of brass _f_ divided into two parts
insulated one from the other by a piece of ebonite _g_; on one side of
this cylinder there are three arms of brass, _h_, _i_, and _k_, and on
the other there are two arms, _l_ and _m_, all of which are insulated
from each other.
[Illustration: AUSTRIAN CIRCUIT CLOSER, MERCURY CIRCUIT CLOSER.
PLATE XIV]
The arm _h_ is close to, but insulated from a metal plate _n_, which
latter is permanently connected with the conducting wire leading from
the firing battery, and thus while in a state of rest is electrically
charged; beyond the arm _i_ is a spring _o_, which is connected with
the earth, and in such a position that when the central portion is
moved round, this spring _o_ comes in contact with the arm _i_, and
the plate _n_ with the arm _h_ simultaneously, and the circuit is thus
completed through earth to the battery, but the current of electricity
does not pass through the fuze. The arms _k_, _l_ on the opposite
sides of the cylinder, and consequently insulated one from the
other, are connected with the fuze, and the arm _m_ is connected with
the earth.
On a further pressure of the vessel on the buffer, the arm _i_ is
pushed beyond the spring, and in contact therewith, and consequently
the circuit by earth to the battery is broken, while the contact of the
arm _h_ and plate _n_ is still retained, and the current is passed by
the arm _k_ through the fuze to the arm _l_, and then to earth through
the arm _m_, thus completing the electric circuit of the firing battery
through the fuze, and to exploding the mine.
The spring acts as a circuit breaker, and by means of an intensity
coil in connection with the firing battery, the current is only passed
through the fuze when at the point of greatest intensity.
By detaching the firing battery, the channel defended by such submarine
mines may be rendered safe.
_Fuze only in Circuit at Moment of Firing it._--One of the principal
objects to be gained by the employment of such an arrangement for the
closing of the electric circuit in connection with submarine mines, is
the prevention of premature explosion from induction which might be
caused by the proximity of any atmospheric electricity, the fuze in
this system being entirely cut out of circuit until the moment when it
is necessary to fire it.
The Austrians employed this form of circuit closing instrument during
the war of 1866, and still continue to use it in connection with their
coast defence by submarine mines.
_McEvoy's Mercury Circuit Closer._--At Fig. 59 is represented a
longitudinal section of a circuit closer of this construction.
It is placed in the mine in such a manner that when undisturbed it
maintains an approximately upright position.
It consists of a metal tube _a_ into which the cup _b_ of vulcanite,
or other insulating material is fixed. The cup is contracted at some
distance from the top by the perforated plug _c_, which is also of
insulating material; _d_ is a metal pin fixed into the bottom of the
cup _b_, it is connected with the wire _e_, which is insulated and
passes to the battery; _f_ is a metal plug closing the tube _a_ and the
cup _b_ at the top; _g_ is a wire attached to the plug _f_, and passing
from it to an earth connection. The cup _b_ is filled with mercury up
to the level of the plug _c_. By the contact of a passing vessel the
instrument would be tilted sufficiently to cause the mercury to flow
into contact with the metal plug _f_, thus completing the electric
circuit and exploding the mine.
This form of circuit closer, though not generally adopted, would, on
account of its being less liable to derangement by the motion of the
waves, or by the explosion of an adjacent or counter mine, seem to
fulfil the many requirements of a circuit closer for general service.
_McEvoy's Weight Magneto Circuit Closer._--This form of circuit closer,
which is shown in section and plan at Figs. 60 and 61, is one of
the most important improvements that has ever been effected in such
apparatus, and bids fair to become universally adopted.
A heavy metal conical shaped weight _a_ (Fig. 60), hollowed out in
its base and working in a ball and socket joint _b_, rests on a solid
brass base _c_, and is so arranged that on the apparatus being struck,
the weight _a_ will fall over, pivoting on one of its supports _d_,
_d_; _e_ is a band of india rubber, encircling the weight _a_, for the
purpose of preventing a jar on its falling against the sides of the
brass cylinder _f_, which contains the weight _a_ and joint _b_. A
brass rod _g_, connected to the ball and socket joint, passes through
the base _c_, through a strong spiral spring _h_ (which latter rests on
an adjusting screw _k_), through a piece of ebonite _l_, which supports
the bobbins and core _m_, _m_^{1}; then between these bobbins _m_,
_m_^{1} through an armature _n_, which is pivoted at _p_; and lastly
through a slight spiral spring _o_, which is kept in position by the
adjusting screw _i_.
The armature _n_ is fitted with a small piece of brass _r_, so arranged
that when it (the armature) is in the position shown in Fig. 60, this
piece of brass _r_ does not make contact with the two strips of metal,
_s_, _s_, between which it, _r_, works; but when the armature _n_ is in
contact with the cores of the bobbins _m_, _m_^{1}, then the piece of
brass _r_ makes contact with the metal strips _s_ _s_, and so makes a
short circuit for the electric current. An ordinary telephone _t_, Fig.
61, in which some small shot, bells, &c., are placed, is fixed to the
top of the brass cylinder _f_.
_Action of Circuit Closer._--The action of this apparatus is as
follows:--
On the mine carrying this form of circuit closer being struck by a
passing vessel, the weight _a_ is caused to fall over towards the side
of the brass cylinder _f_, thus allowing the strong spiral spring _h_
to act on the brass rod _g_ in an upward direction, by which means the
armature _n_ is brought into contact with the soft iron cores of the
bobbins _m_, _m_^{1}.
[Illustration: M^{c.}EVOY'S MAGNETO ELECTRO CIRCUIT CLOSER.
PLATE XV]
The connections of the wires are made as follows:--
The line wire _w_ is led through the base of the apparatus and
connected to a piece of brass under the ebonite support _l_, in
connection with one of the wires of the bobbin _m_, the other wire
of which is attached to the metal strip _s_; the wires of the bobbin
_m_^{1} are connected, the one to the metal strip _s__{1}, the other
to a piece of brass under the ebonite support _l_; from this latter
piece of brass a wire _w__{1} is led to the brass screw _x_. The wires
_w__{2}, _w__{3}, from the fuzes are led, the one to the brass screw
_x_, the other to a screw _y_, which forms through the metal of the
apparatus the earth plate. One of the wires of the telephone _t_ is
connected to the brass screw _x_, the other _w__{4} is connected to
the piece of brass to which the line wire _w_ is also attached. While
the circuit closer remains in a state of rest, the current from the
signalling battery flows along the line wire _w_, up the telephone wire
_w__{4}, through the telephone which has a high resistance, then by the
wire _w__{2} through the fuzes, and to earth by the wire _w__{3}.
On the circuit closer being struck, by which cause the armature _n_ is
brought up to the cores of the bobbins _m_, _m_^{1}, and the piece of
brass _r_ in contact with the metal strips _s_, _s__{1}, the signalling
current, instead of circulating through the high resistance of the
telephone _t_, passes round the bobbin _m_, down the metal strip _s_,
across the brass piece _r_, up the metal strip _s__{1}, round the
bobbin _m__{1} (thus forming an electro magnet of _m_, _m__{1}), and by
the wire _w_, direct through the fuzes to earth, and so explodes the
torpedo. The effect of the telephone resistance being cut out, is to
strengthen the signalling current, and enable it to work the shutter
apparatus and so throw the firing battery in circuit and explode the
mine.
The advantages of this circuit closing apparatus are:--
1.--Simplicity.
2.--Compactness.
3.--Increased certainty of action, due to the sustained
contact of the armature _n_, on the apparatus being
struck.
4.--Additional means of testing a system of electrical
submarine mines, which is afforded by the telephone:--
When this form of circuit closer is put in action by a friendly vessel
coming in contact with it, or when experiments are being made, the
signalling current must be reversed, so that no doubt may exist as to
the armature _n_ having dropped, on the apparatus coming to rest.
The telephone test indicates whether the circuit closer is in position
or not, the shot, &c., within the telephone being shaken about by the
movement of the buoyant circuit closer, the noise so created is readily
distinguished by the receiving telephone at the station.
Another form of submarine mine is that known as the "Electro
Mechanical" mine. The difference between this form and an ordinary
mechanical mine is, that the exploding agent is electricity, and that
it may be converted into an electro contact mine if desirable.
_Description of a Russian Electro._--The electro mechanical mine,
used by the Russians during the late Turco-Russian war, is shown in
elevation and section at Figs. 62 and 63.
_Mechanical Submarine Mine, used by them during the late Turco-Russian
War._--_A_ is the conical shaped case; _B_ the loading hole; _C_ the
base plug; _D_, _D_, &c., are five horns, screwed into the head of the
case _A_; these are composed of a glass tube _A_, containing a chlorate
of potash mixture, enclosed in a lead tube _B_, over which is screwed a
brass safety cylinder _C_; when ready for action this latter tube _C_
is removed; directly beneath each of the horns _A_, on the inside of
the case, as at _E_, is a thin brass cylinder, closed at one end by a
piece of wood _d_, and containing several pieces of zinc and carbon,
arranged in the form of a battery, the zinc and carbon wires _z_ and
_x_ being led through the piece of wood _d_; _F_ is a copper cylinder
containing the priming charge of gun-cotton _g_, and detonating fuse
_f_; the terminals of the fuze are connected to two insulated wires,
_w_ and _w__{1}, the former of which is led direct to the loading hole
_B_, and attached on the inside to the five zinc connecting wires _z_,
&c.; the latter is attached to one end of a safety arrangement _S_, the
other end of which is connected to the wire _w__{2}, which is attached
on the inside to the carbon wires _x_, &c.; the safety arrangement _S_
consists of an ebonite cylinder, containing a brass spiral spring fixed
to one end of it, and pressing against a brass plate at the other,
thus preserving a metallic connection between the wires _w__{1}, and
_w__{2}; the mine is rendered inactive by pressing the spring down, and
inserting a piece of ebonite between it and the plate.
_Its Action._--The action of this form of electro mechanical submarine
mine is very simple; the brass safety cylinders _c_, _c_, &c., being
removed on a vessel striking either of the horns, _D_, _D_, &c., the
lead tube _b_ is bent, causing the glass tube _a_ to be broken, and
the mixture contained therein to flow into the cylinder _E_, instantly
generating a current of electricity in the zinc carbon battery, and
exploding the mine.
_Mode of Converting into an Electro Contact or Observation Mine._--To
convert this mine into an electro contact one, it is only necessary to
connect the wires _w__{1} and _w__{2} to other wires leading from the
shore; also by replacing the horns _D_, _D_ by solid brass screw plugs,
the mine may be converted into an ordinary observation one. In this
case the two wires _w_ and _w__{1} attached to the fuze _f_, terminals
would have to be connected to the observation instruments on shore.
_Turkish Vessel sunk._--It was by means of one of these electro
mechanical mines, that the Turkish gunboat _Suna_ was sunk at Soulina.
Firing by observation, that is to say, effecting the ignition of an
electrical submarine mine at the precise moment of a hostile vessel
being vertically over it, through the agency of one or two observers
stationed at a very considerable distance from the mine, should, with
the very perfect self-acting circuit closers that exist at the present
time, be resorted to only in very exceptional cases, or in connection
with the self-acting system.
There are two defects, which are common to all methods of firing
submarine mines by observation, and these are:--
1.--At night time, or in foggy weather, it cannot be
employed.
2.--It is necessary to employ at least two observers,
at a considerable distance apart, who to effect a
proper action at the right moment, must work in perfect
unison. These defects alone are sufficient to explain
the preference given to a self-acting method of closing
the electric circuit at the precise moment of a vessel
being in position over a mine by those governments who
have adopted electrical submarine mines as a means of
coast defence.
_Methods of Firing by Observation._--There are several methods of
firing by observation, of which the following are the ones principally
used:--
1.--By pickets or range stakes.
2.--By cross bearings.
3.--By intersectional arcs fitted with telescopes.
4.--The Prussian system.
_Intersection by Pickets or Range Stakes._--In narrow channels and at
short distances, this system of ascertaining the relative position
of a hostile vessel and a submarine mine may be used, provided that
skilled and careful men are employed to work it. Two or more pickets
or stakes are arranged in front of the firing station in such a manner
that a vessel passing up the channel on the prolongation of these
stakes will be over a mine. This arrangement should of course always be
considered as an extempore one; it was used on several occasions by the
Confederates during the American civil war.
_Firing by Cross Bearings._--The simplest method of so determining
the relative position of a vessel and a submarine mine, and exploding
it at the right moment, is that in which observers are placed on
the prolongation of the mines. This mode is shown at Fig. 64, where
_m__{1}, _m__{2}, _m__{3}, &c., and _n__{1}, _n__{2}, _n__{3}, &c.,
are the mines; _A_ and _B_, the points in prolongation of the mines
where the observers are stationed; _D_ the firing battery, and _s_, and
_s__{1} two hostile vessels.
At the stations _A_ and _B_ firing keys are placed, at the former one
for each separate mine, perfectly distinct and insulated from each
other, at the latter a single key. The pivot points of the series of
keys at _A_ are connected by separate wires to one pole of the firing
battery _D_, the other pole of which is connected by a single cored
insulated cable to the pivot point of the key at _B_; the contact
points of the series of keys at _A_ are connected by separate line
wires as _A m__{1}, _A m__{2}, _A m__{3}, &c., to the different mines,
while the contact point of the key at _B_ is put to earth. Thus it will
be seen that, in the case of the row of mines, _m__{1}, _m__{2}, &c.,
unless the key at _B_, and the key at _A_, of either of those mines
are both pressed down at the same instant, no current can pass, and
therefore none of those mines can be exploded.
[Illustration: RUSSIAN SUBMARINE MINE, FIRING BY OBSERVATION.
PLATE XVI]
In the case of the vessel _S_, though at _C_, she is on the
prolongation of the line _A m__{5}, _C_, and therefore the key of the
mine _m__{5}, is pressed down at _A_, yet not being on the prolongation
of the line _B_, _E_, the key at _B_ is not pressed down, therefore the
firing battery is not thrown in circuit, or the mine _m__{5} exploded,
but when the vessel _s_ reaches the position _N_, that is over the mine
_m__{3}, she being on the prolongation of the lines _A m__{3}, and _B
E_, the key (_m__{3}) at _A_, and the key at _B_ would both be pressed
down, and therefore the mine _m__{3} exploded, and the ship destroyed.
In the case of a vessel passing through an interval between any two
mines at such a distance as to be out of the radius of destructive
effect of either of the mines belonging to the first row (which is
shown at _s__{1},) only the key at _B_ would be pressed down, and thus
the vessel enabled to pass safely through, but only to come to grief
at the second or third row of mines, provided they have been properly
placed, and separate though similar arrangements as in the case of the
line of mines, _m__{1}, _m__{2}, &c. have been made.
_Firing by a Preconcerted Signal._--At Fig. 65 is represented a
somewhat similar, though a much simpler plan of the foregoing system,
by employing a preconcerted signal at the station _B_ in the place of
the firing key and insulated cable, as in the former case. The only
material difference in the arrangement of these two methods, is that
in the latter case the pole of the firing battery at _A_, which in
the former case was connected to the firing key at _B_, is put direct
to earth. As will be readily understood, this latter system requires
great coolness and nerve on the part of the operator at _A_, who has
not only to watch the vessel passing across his intersections, but
also to be on the alert to receive the signal from the observer at
_B_. Should it ever be necessary to adopt this latter system, it will
be found advisable to employ two men at station _A_, one to watch
station _B_, the other to attend to the firing key and intersections.
A separate signal-flag for each line of mines, and also a separate
firing arrangement, would be required. As in many cases it would not
be practicable to have a station in such an advanced position as at
_B_, in Figs. 64 and 65, on account of the danger of its being cut off
by an enemy, another combination becomes necessary. In this instance
the station _B_ is placed on the opposite side of the river, &c.,
to that on which the station _A_ is placed, and a series of firing
keys, instead of a single one, is here used, necessitating a multiple
cable between the stations _A_ and _B_, in the place of single cored
cable; the manner of manipulating this method is very similar to that
previously described.
_Firing by Intersectional Arcs fitted with Telescopes._--The
foregoing methods of firing by cross bearings are replete with
many serious defects, to remedy which, to a considerable extent,
special arrangements have been devised, that is, the employment of
intersectional arcs fitted with telescopes at the stations _A_ and _B_.
Figs. 66 and 67 show the arrangements of these arcs, the former being
the one used at the firing station _A_, the latter at the converging
station _B_. At each station one arc is provided for each row of mines
placed in position. The firing arc Fig. 66 consists of a cast iron
frame _a_, with three feet _b_, _b_, _b_, these being provided with
levelling screws.
To ascertain when this frame is level, a circular spirit level is
attached thereto, a telescope _d_ provided with one horizontal and
three vertical cross wires, supported on Y's, admitting of vertical
motion and attached to an upright _e_. A mill-headed screw _f_ enables
the telescope _d_ to be raised or lowered; the telescope, which is
rigidly connected to a vernier _g_, traversing over a graduated arc
_h_, can be moved rapidly in a lateral direction by means of a rack
and pinion arrangement _i_, and it can be clamped in any position by
means of the screw _h_. Sights are fixed on the telescope in a vertical
plane passing through its axis. To the outer rim of the frame of the
arc, which is smooth, are secured the sights _l l_ (shown on a large
scale at Fig. 68), to give the direction of the mines. These sights are
provided each with a brass point of V form, _m_, and a binding screw,
_n_, in metallic connection with each other, but insulated by means of
an ebonite plate from the rest of the metal of the sight. One end of a
short piece of insulated wire is attached to the binding screw _n_, and
the other passes through a hole in the base of the sight and projects
below it; _o_ is a brass tube rigidly connected to and moving with the
upright carrying the telescope _d_, and projecting in front of this
latter. A brass spring _p_ (see Fig. 69) is attached to, but insulated
from the outer extremity of this tube, and is so arranged as to make
contact with the V point _m_ on the sight, by means of a corresponding
projection fitted to its under side. An insulated wire passing the tube
_o_, the outer end of which is connected to a screw on the spring _p_,
forms a metallic connection between this projection and the firing key.
At Fig. 68 is shown an enlarged view of the front of the sight; in
addition to the V projection _m_, and binding screw _n_, it is fitted
with a capstan-headed screw to bear against the inner rim of the frame,
and a thin wire upright _t_ for giving the alignment of the mine, to
which a disc is attached, on which the number of the mine is affixed.
When the distance between the station and the mine is only about one
mile, an ordinary eyepiece is used in the place of the telescope _d_.
At Fig. 67 is represented the arc employed at the converging station,
which with the exception of there being no tube _o_, and only one
sight, is precisely similar in construction to the one used at the
firing station, and which has been described.
[Illustration: APPARATUS FOR FIRING BY OBSERVATION.
PLATE XVII]
_Application of the Intersectional Arc Method._--The application of the
method of firing by observation, by means of intersectional arcs fitted
with telescopes, is shown at Fig. 70. _C_, _D_, and _E_ are three of
the larger kind of arcs, one being used for each row of mines at the
firing station _A_. At the converging station _B_, one of the smaller
arcs is used for each row of mines, as shown at _F_, _G_, and _H_.
_S_, _S__{1}, _S__{2}, are the signalling apparatus, the _F_ terminals
of which are connected to the sights _l_, _l_, _l_, Fig. 69, of arcs
_C_, _D_, _E_. Firing keys _a_, _a_, _a_ at station _A_ are connected
to each arc, and to three of the cores of the cable connecting the two
stations _A_ and _B_, respectively. At the converging station _B_,
three firing keys _b_, _b_, _b_ are connected to earth and to three
cores of the connecting cable respectively. The remaining core of this
cable is connected to the recording instruments _d_, _e_. The action of
the arcs, &c., will be readily understood from the diagram at Fig. 70.
This arrangement does not interfere with the action of the circuit
closer, as all that is effected by the observing arc circuit is to put
the signalling battery current at the converging station _B_ to earth
instead of at the circuit closer.
_Prussian System of Firing by Observation._--The principle on which
this system is based, depends upon the proposition that if _c d_, in
the triangle shown in Fig. 71, be always kept parallel to _H B_, then
_A c_, _c d_, _d A_ bear exactly the same proportion to each other as
_A B_, _B H_, _H A_ do to one another; so that by means of the small
triangle _A d c_, the lengths of the sides of the large triangle _A
B H_ can be obtained, and hence the position of the point _H_, the
base _A B_ being of course known. In Fig. 71 at _A_ there is a slate
table representing the roadstead, and upon it the exact position of
every torpedo is laid down, corresponding to their position in the
roadstead. At _A_ and _B_, 500 yards apart, telescopes having cross
wires are placed; at _A_ a long narrow straight-edged strip of glass
_A d_ is arranged to move in unison with the telescope at _A_; and by
the application of dynamo electricity, a similarly constructed piece of
glass _c d_ moves in exact unison with the telescope at _B_, and having
its pivot at _C_; that is to say, _C d_ keeps parallel with _B H_, the
line of sight of the observer at _B_.
Then if the observers at _A_ and _B_ have got a ship in their
telescopes, the point of intersection _d_ of the two pieces of glass _A
d_ and _C d_ gives the position of the ship on the slate table at _A_,
and when this point _d_ comes over the position of any one mine on the
slate, it is known that the ship is over that particular mine in the
harbour, and she may be destroyed accordingly, by throwing the firing
battery into circuit.
By the employment of electricity and a mirror, the great defect of this
method, viz., the necessity of employing four people to manipulate it,
would be remedied. The foregoing is a modification of Siemens's method
of ascertaining distances at sea, &c.
_Rules observed in Planting Mines._--In placing a system of submarine
mines in position, the following are some of the chief points to
be attended to, this work depending in a great measure on local
circumstances, and on the method that is to be adopted in exploding and
mooring them:--
1.--The plan of defence must be carefully laid down
on a chart, on a scale of not less than six inches
to the mile, and on this plan are to be marked the
sites of the observing stations, the positions of each
mine, circuit closer, and junction box, with their
corresponding numbers, and also of the electric cables.
2.--The position of each mine having been determined,
should be marked off by buoys.
3.--The utmost care should be taken to lay the electric
cables, so that they shall be as far as possible away
from the mines in the vicinity of which it may be
necessary to take them, so as to lessen the liability
of injury to them, by the explosion of the latter.
4.--The electric cables should be laid parallel, and
never be allowed to cross directly over each other,
otherwise the operation of underrunning them will be
much complicated, also a certain amount of slack should
be allowed to facilitate in picking the cables up for
repair, &c.
5.--Every manner of device is to be used to conceal the
electric cables, such as laying dummies, making detours
inland, &c.
6.--All marks indicating position of the mines to be
removed, after the mines have been placed in position.
7.--The identity of each cable and mine to be very
carefully preserved throughout, by means of a number.
8.--A number of electro contact mines should be
placed in advance of the leading line of mines, at
irregular intervals, to prevent the enemy, having once
ascertained the position of one mine of a line, from
knowing within limits the position of the others of
that line.
[Illustration: SYSTEMS OF DEFENCE BY SUBMARINE MINES.
PLATE XVIII]
In connection with a system of defence by electrical submarine mines,
the following batteries are required:--
1.--Firing battery.
2.--Signalling, or shutter battery.
3.--Testing battery.
4.--Telegraph battery.
_Firing Battery._--The firing battery should be suited to the nature of
the fuze employed, and should possess considerable excess of power to
enable it to overcome accidental defects, such as increased resistance
in the various connections, or defective insulation in the line wire,
&c.
As platinum wire or low tension fuzes are now universally adopted as
the mode of ignition for submarine mines, it will be only necessary
to describe those electrical batteries which are most suitable as an
exploding agent in connection with such fuzes; these are as follows:--
1.--Siemens's dynamo low tension machine.
2.--Von Ebner's Voltaic battery.
3.--Chromic acid or Bichromate Voltaic battery.
4.--Leclanché's Voltaic battery.
_Siemens's Low Tension Dynamo Electrical Machine._--This instrument
consists of an electro magnet and an ordinary Siemens armature, which,
by the turning of a handle, is caused to revolve between the poles of
the electro magnet. The coils of the electro magnet are in circuit with
the wire of the revolving armature, and during rotation the residual
magnetism of the soft iron electro magnet cores at first excites weak
currents which pass into the electro magnet coils, increasing the
magnetism of the core, thus inducing still stronger currents in the
armature wire. This accumulation by mutual action goes on until the
limit of magnetic saturation of the iron cores of the electro magnets
is reached.
By the automatic action of the machine, the powerful current so
produced is sent into the leading wire or cable to the fuze to be
exploded.
In this apparatus the electric current passes continuously through the
line wire until a sufficiently powerful current is generated to heat or
fuze the bridge of the fuze, and so ignite the gun-cotton priming. The
coils of the armature and electro magnets are wound with wire of large
diameter, to a total resistance of 8 to 10 Siemens units, or 7·6 to 9·5
ohms, in about 2,000 windings.
With a platinum wire weighing 1·65 grains per yard, 6-1/2 inches can be
fuzed on short circuit, and 14 inches can be heated to redness.
The total weight of this machine, which is manufactured by Messrs.
Siemens Brothers, is about 60 lbs.
_Advantages of Siemens's Dynamo Electrical Machine._--The advantages of
such a machine over Voltaic apparatus are:--
1.--The absence of chemical agents.
2.--There is less liability to get out of order.
3.--No special knowledge is required to work them, or
to keep them in order.
4.--Greater durability.
The great defect of this and all similar machines is that the electric
force has to be developed by turning a handle for a certain time
before it is possible to generate a current sufficiently powerful to
ignite a fuze, which defect, in connection with a system of defence
by self-acting submarine mines, particularly at night, renders them
inferior to Voltaic batteries, as under such circumstances, an
apparatus is required that will cause an electric current to flow at
any moment when the circuit is completed.
The application of steam power would to a certain extent remedy the
above-mentioned defect, but the cost of such a method, compared to
that of a Voltaic arrangement, would be far too great to allow of its
superseding the latter arrangement.
_Von Ebner's Voltaic Battery._--This form of Voltaic battery, which
may be considered as a modification of that known as Smee's, was
designed by Baron von Ebner, colonel of the Austrian imperial corps of
engineers, for use in connection with the Austrian system of submarine
defence, by self-acting electrical mines.
A section of one of these cells is shown at Fig. 72. It consists of a
glass vessel _a_, to contain the diluted sulphuric acid, within which
is suspended a plate _b_ of platinised lead, which is bent round into
a cylindrical form to fit close around the inner surface of the glass
vessel. In the centre of this latter is hung a porcelain perforated
cup _c_, containing some cut-up zinc and mercury to keep it (the zinc)
amalgamated. The top of each cell is furnished with a porcelain cover,
through which the wires attached to the positive and negative poles of
the cell project.
Due to the large quantity of liquid contained in the cell, the
tendency to alter its internal resistance is retarded; also by the
arrangement of the porcelain cup, above detailed, the consumption
of zinc and mercury, which in an ordinary Voltaic battery is very
considerable, is materially diminished.
_Chromic Acid or Bichromate Battery._--This form of battery is very
similar to Grove's, the difference being that, in the place of the
nitric acid as the exciting liquid, either chromic acid, or a solution
of bichromate of potash, sulphuric acid and water is substituted.
A form of this battery, as designed by Dr. Hertz, is used in connection
with the German system of torpedo defence.
_Leclanché Voltaic Battery._--This form of Voltaic battery was invented
by M. Leclanché, some twelve years ago. At Fig. 73 is shown a cell of
this battery in its original form. The positive pole _a_ consists of a
plate of graphite in a porous pot _b_, and surrounded by a mixture of
peroxide of manganese and graphite. The negative pole _c_ is a rod or
pencil of amalgamated zinc. The whole is enclosed in an outer vessel of
glass _d_ containing a solution of sal ammoniac.
A modified form of the Leclanché cell as used in a firing battery is
shown at Fig. 74. It consists of an ebonite trough or outer vessel _a_
about 16" long, 9" deep, and 2-3/4" wide. The negative pole or zinc
plate _b_ is of similar shape to the trough _a_, but with its base
removed, and does not fit the trough exactly, the space between it and
the trough being left to ensure the former being completely surrounded
by the sal ammoniac solution; the positive pole, or carbon element,
consists of four gas carbon plates _c_ attached together at their head
by means of lead, and enclosed in a flannel bag, in which they are
firmly embedded in the peroxide of manganese mixture; the positive
element is of such a shape that it fits loosely between the sides, and
is nearly of the same height as the zinc plate.
The object of such a form of cell was to obtain an electric current of
large _quantity_, with as few cells as possible, by which means the
loss of power which might occur from the employment of a great number
of small cells is avoided.
_Advantages of a Leclanché Firing Battery._--The advantages of the
Leclanché firing battery are:--
1.--The absence of chemical action when the battery
circuit is not complete, and consequently there is no
waste of material.
2.--Requires little or no looking after.
3.--It may be kept ready for action in store without in
any way deteriorating.
4.--It is comparatively very cheap.
These advantages combine to make a Leclanché battery the most suitable
of any other form of electrical battery for use as the exploding agent
for electrical submarine mines, and it is now universally used for such
purposes.
_Signalling Battery._--The signalling battery should be so constituted
as to be capable of working the electro magnet of the shutter apparatus
effectually when the circuit is closed direct to earth, and yet not so
powerful as by the continuous passage of the current generated by it to
fire the fuze in the mine. In the case of a platinum wire fuze being
in the circuit, plenty of power may be given to the battery without
fear of a premature explosion from this cause, but in the case of a
high tension fuze it is necessary to be very careful in order to guard
against such a contingency.
As in the case of a signalling or shutter battery, the electric current
will be continually flowing, it is necessary to employ a constant
battery, or one that requires least trouble and expense to maintain it
in working order, and it is for this reason that a modified form of
Daniell battery has been adopted to work the shutter apparatus.
_Daniell Signalling Battery._--At Fig. 75 is shown the manner of
arranging a Daniell cell. A glass or porcelain vessel _a_ contains a
saturated solution of sulphate of copper, in which is immersed a copper
cylinder _b_ open at both ends and perforated by holes; at the upper
part of this cylinder there is an annular shelf _d_, also perforated
by holes, and below the level of the liquid; this is for the purpose
of supporting crystals of sulphate of copper for the replacing of that
decomposed as the electrical action proceeds. Inside the cylinder _b_
is a thin porous vessel _c_ of unglazed earthenware; this contains
either water, or a solution of common salt, or dilute sulphuric acid,
in which is placed the cylinder of amalgamated zinc _e_. Two strips of
copper _p_ and _n_, fixed by binding screws to the copper and to the
zinc, serve for connecting the elements in series, or otherwise.
For the purposes of testing, either the Leclanché or Daniell battery
specially arranged, or the Menotti battery, which is really a
modification of the Daniell, may be used.
[Illustration: FIRING BATTERIES, TESTING BATTERIES.
PLATE XIX]
_Description of a Menotti Cell._--A Menotti cell, shown at Fig. 76,
consists of a copper cup containing some crystals of sulphate of copper
and covered with a fearnought diaphragm _a_, placed at the bottom of
an ebonite cell _b_; over this cup is put some sawdust, and resting on
top of this is a disc of zinc _c_ on another piece of fearnought. The
upper portion of the zinc and its connection with the insulated wire
are carefully insulated. Fresh water poured on the sawdust renders the
battery active.
_Description of a Menotti Test Battery._--Fig. 77 represents a plan
of the top of such a test battery with a 20-ohm galvanometer attached
thereto. The connections are made as follows:--
One of the wires _w_ of the object to be tested is attached to the
terminal _f_, which is also connected by an insulated wire to the
copper cup _a_; the other main wire _w__{1} is attached to the terminal
_g_ of the galvanometer; _h_, the other terminal of the galvanometer,
is connected by a short piece of wire _k_ to the terminal _l_ of the
contact key _m_; and the contact point _n_ is in connection with the
zinc plate _c_; thus the current from the battery flows along the wire
_w_ through the object to be tested, back along the wire _w__{1},
through the coils of the galvanometer, along the wire _k_ to the
contact key _m_, and if this is pressed down to the zinc plate _c_, so
completing the circuit.
To steady the needle of the galvanometer a bar magnet is used, which is
inserted in the space _r_. The whole of the apparatus is enclosed in a
leathern case fitted with a cover and strap.
This is a very compact and simple form of test battery, and will be
found extremely useful in boats, &c., when placing mines in position.
_Telegraph Battery._--For the purposes of telegraphing between torpedo
stations, &c., a form of Leclanché battery, known as No. 3 commercial
pattern, is generally used.
_Voltaic Batteries._--The following points in connection with the
use of voltaic batteries, which are taken from Beechey's 'Electro
Telegraphy,' should be carefully observed:--
1.--Each cell of a battery should be carefully
insulated.
2.--The floors and tables in the battery room should be
kept scrupulously clean and dry, so as to prevent the
least leakage or escape of the current.
3.--The plates of a battery should be clean.
4.--Porous cells should be examined, and cracked ones
replaced.
5.--No sulphate of zinc or dirt should be allowed to
collect at the lips of the cells.
In the case of a Daniell battery--
1.--The solutions should be inspected daily, and
crystals of sulphate of copper added as required.
2.--The zinc plate must not touch the porous cell, or
copper will be deposited on it (the zinc).
3.--The battery should be charged with sulphate of zinc
from the first.
4.--The copper solution must be watched and prevented
from rising over the edge of the porous jar, the
tendency of such solutions being to mix with each other
by an action termed _osmosis_.
These being in addition to foregoing general directions for Voltaic
batteries.
_Defects in a Voltaic Battery on its Current becoming Deficient._--On
the electric current of a Voltaic battery becoming deficient, the
following defects should be looked for:--
1.--Solutions exhausted; for instance, sulphate of
copper in a Daniell's entirely or nearly gone, leaving
a colourless solution.
2.--Terminals or connections between the cells
corroded, so that instead of metallic contact there are
oxides of almost insulating resistance intervening in
the circuit.
3.--Cells empty, or nearly so.
4.--Filaments of deposited metals stretching from
electrode (pole) to electrode (pole).
Also intermittent currents are sometimes produced by loose wires or
a broken electrode, which alternately makes and breaks contact when
shaken. Inconstant currents are also sometimes produced when batteries
are shaken. The motion shakes the gases off the electrodes, thus
increasing temporarily the electro-motive force of the battery.
_Firing Keys and Shutter Apparatus._--The following is a description of
the various firing keys and shutter signalling apparatus, which is used
in connection with a system of electrical submarine mines. By means of
the former the firing or other batteries may be thrown into circuit
at will, whilst by means of the latter the firing battery is thrown
in circuit without the aid of an operator, and a signal at the same
instant given, indicating that a certain mine of the system has been
struck.
_Description of a Series of Firing Keys._--At Fig. 78 is shown a plan
and section of a series of firing keys as arranged for firing several
mines by observation.
It consists of a strong wooden frame _a_, of a convenient form for
the purpose of attaching it to the firing table by screws through the
holes _b_, _b_. On this frame a series of keys _c_, _c_, _c_ are fixed
at convenient intervals. These consist of a strong brass spring firmly
screwed to a series of brass plates _d_, _d_, _d_ on the front of the
wooden box _a_. From these latter short copper wires pass through the
woodwork, and of such a length that, when required, the mine wires may
be easily attached by means of binding screws, as shown at _f_. The
inner end of each key is fitted with an ebonite knob (which is shown
at _c_ in the section) to insulate the hand of the operator when using
the key. On the frame, and directly under each of the ebonite knobs,
are arranged a series of metallic points _g_, _g_, _g_, so placed that
on either of the keys _c_ being pressed down, a perfect contact is made
between it and its respective metallic point; _h_, _h_, _h_ are copper
wires leading from the metallic points _g_, _g_, _g_ through the box,
and of such a length that binding screws _f_, _f_, _f_ can be easily
attached to them when necessary.
A single firing key of an improved form is shown at Fig. 79. It
consists of a strong wooden box _a a_, weighted at the bottom with
lead in order to steady the key on the table, &c., on which it may be
placed; on the inside of the bottom of the box is fixed a piece of
ebonite, by which means the metallic point _b_, and the terminal of the
firing key _c_, are insulated from each other; _d d'_ are two terminals
at the end of the box, to which the circuit wires are attached, one
of these terminals is connected in metallic circuit to the firing key
at _c_, the other one to the metallic point _b_; a wooden cover _h_,
fitted with a catch _k_, protects the connections of the wires; by
means of a plate, and catch _e e_, the key can be rendered inactive,
thus preventing the danger of a premature closing of the electric
circuit; by means of a spring _s_ a break is always established between
the key and the metallic point. It is immaterial to which of the two
terminals _d d'_ either wire is connected.
_The Morse Firing Key._--This form of key is so well known in
connection with the Morse telegraph, that it is not necessary to
describe it.
It is usually employed in torpedo work in connection with a testing and
firing table.
_The Shutter Apparatus._--The shutter signalling and firing apparatus
was devised to enable the firing battery current to be thrown in
circuit without the aid of a personal operator, the signalling current
(which is always kept in circuit) at the same instant ringing a bell,
by which is known the particular mine that has been struck.
At Fig. 80 is represented a diagram of such an apparatus. _a_ is an
armature working on a pivot between the two horns of an electro magnet
_b b_, and held in position by a spiral spring _c_; the latter is in
connection with a regulating screw, by which more or less pressure may
be brought to bear in an opposite direction to that of the attractive
action of the electro magnet. A stud _i_ regulates the distance to
which the armature may be drawn back; _d_ is a shutter on which a
reference number for each mine should be indicated, attached to a
lever pivoted at the point _e_, the inner arm of which is just long
enough to catch under the point of the armature _a_; when a current of
sufficient strength is passed through the coils _b b_ of the electro
magnet, the armature _a_ is attracted, releasing the lever attached
to the shutter _d_, which by its own weight falls into the position
shown by the dotted lines. _f_ and _g_ are two mercury cups, the former
being in connection with the signalling current, and the latter with
the firing current. When the lever is horizontal and the shutter drawn
up and ready for action, the circuit of the signalling battery _s_ is
completed through the mercury cup _f_, along an arm _h_ of the lever
to the pivot _e_, and thence to the mine by the line wire _w_. When
the circuit closer is struck by a passing vessel, and consequently the
shutter thrown into the position shown by the dotted lines, another
arm _k_, a prolongation of the lever, falls into the mercury cup _g_,
which latter is in connection with the firing battery _F_. The armature
_a_ is prevented from coming into actual contact with the horns of the
electro magnet by two small studs. The object of this is to prevent any
effect of residual magnetism which might otherwise interfere with the
rapidity of action of the armature when released and drawn back by the
spring _c_.
[Illustration: FIRING KEYS, SHUTTER APPARATUS.
PLATE XX]
_The object of employing Mercury Cups._--Mercury cups were devised in
the place of the springs used in connection with the original design of
a shutter apparatus, for the reason that electrical circuits dependent
on the pressure of springs are always liable to interruption from dirt
or oxide intervening between the points of contact.
_Shutter Apparatus used with a Circuit Breaker._--When the circuit
breaking system is used with the shutter signalling apparatus, the
action of the armature in releasing the lever must be reversed; that is
to say, that when the current is passing and the armature _a_ attracted
to the electro magnet _b b_, the shutter _d_ must be held up, and when
the current ceases, and the armature _a_ drawn back by the spring _c_,
the lever must be released, and the shutter allowed to fall. This is
effected by altering the end of the lever, so that it hooks into,
instead of abutting against the armature _a_.
To each shutter apparatus an electric bell is fitted, by which notice
is given when a circuit closer has been struck. For general service, a
box containing seven such shutter signalling and firing apparatus has
been adopted, a plan of which is represented at Figs. 81, 82 and 83.
The connections of the different circuits are as follows:--
The insulated wire of the upper bobbin of the electro magnet is
connected to the spring of the armature; the pivot of the lever is
connected with the right-hand terminal _B_, or main line connection
on the top of the box; the insulated wire from the lower bobbin is
connected to the middle brass plate _k_ in the front ledge of the
apparatus, the circuit from _B_ to _k_ being thus completed. The front
adjoining brass plate _A_, provided with a terminal, is connected with
the negative pole of the signalling battery, the positive pole being
put to earth.
On a brass plug being put in the hole _l_, the signalling current will
flow to the plate _k_, thence through the lower and upper bobbin to
the spring of the armature, along the latter to the shutter lever, and
from the pivot through the main line wire to the mine. The innermost
brass plates _H H_ are all connected in the same metallic circuit, and
to them are attached by means of the binding screw _D_ the test battery
and galvanometer. Thus on the brass plug being removed from _l_, and
placed in _m_, the signalling battery is cut out of circuit, and the
test battery thrown in. In this way the condition of each individual
mine may be ascertained while the connections of the remaining mines
are left undisturbed. The positive pole of the firing battery (the
negative being to earth) is connected to the terminal _S_ at the
right-hand corner of the lower ledge of the box; the plate to which the
terminal _S_ is fixed is divided at _G_, the left-hand portion being
connected to a bar which runs horizontally the whole length of the
box, and in metallic connection with each mercury cup _g_, Fig. 80. A
brass plug is placed in the hole _G_, and when from any cause the lever
drops, the firing battery will be thrown into circuit, and the mine to
which the lever that has fallen is attached will be exploded.
_Shutter Instrument and Observing Telescope._--Each mine is given a
number, which is put on the disc of the shutter instrument connected
to it, and also on the corresponding tablet _C_. From the brass plate
in connection with the spring _c_, Fig. 80, a wire is taken to the
terminal _f_, Fig. 81, on top of the box. From this terminal a wire is
led to the connections of the observing telescope, and thus the mines
can be fired by judgment if required, without the aid of the circuit
closer.
The signal battery current is always circulating, even when the system
is in a state of rest, but in consequence of the resistance placed in
this circuit, which may be either a resistance coil in the circuit,
added to the resistance of the fuzes, when high tension fuzes are used,
or only the former resistance in the case of low tension fuzes, this
current is too feeble to form an electro magnet; directly, however,
a circuit closer is struck, this resistance is cut out, and thus the
signal battery current becomes sufficiently powerful to work the
electro magnet of that particular mine.
The circuit of the signal battery, and that to the observing telescope,
are broken the instant the lever commences to fall.
To enable the apparatus to be used on the circuit breaking system, a
spare lever _E_ is provided for that purpose with each box.
The object to be gained by a system of testing is to ascertain the
condition of the electrical submarine mines placed in the defence of
a harbour, &c., and should there exist any fault, not only to detect
its exact position and cause, but also its magnitude, so that it may
be at once determined whether it is necessary to remedy the fault, or
whether the electrical apparatus is sufficiently powerful to overcome
the defect.
_Tests._--There are two distinct kinds of tests, viz.:--
1.--Mechanical tests.
2.--Electrical tests.
[Illustration: SHUTTER APPARATUS.
PLATE XXI]
Mechanical tests are applied to ascertain that the mechanical
arrangements of the shutter apparatus, circuit closers, and all similar
appliances work efficiently and easily; that the several parts of the
mine case when put together for service are thoroughly watertight;
that the chains, wire cables, and ropes in connection with the mooring
apparatus are of sufficient strength to perform the work required of
them; that the weights of the anchors, or sinkers, are such as to keep
the mines in position after submersion; and that the case of the mine
be sufficiently strong to enable it to bear the external pressure due
to the depth at which it may be submerged for a considerable time
without any leakage.
The foregoing tests of the mine case and moorings would of course be
performed during the process of manufacture, but to prevent any chance
of failure they should be repeated before being employed on actual
service.
_Electrical Tests._--Electrical tests are those which are applied
to the several component parts of the system, to ascertain that the
electrical conditions necessary to a successful result exist.
The importance of being able to carry out the above in its entirety
is understood when it is remembered that a submarine mine becomes
practically valueless unless it acts efficiently at the single instant
of time that it would be required so to do.
_List of Instruments used in Testing._--The following are some of the
instruments that are employed in connection with a system of electrical
tests:--
1.--Thomson's electrometer.
2.--Thomson's reflecting galvanometer.
3.--Astatic galvanometer.
4.--Differential galvanometer.
5.--Detector galvanometer.
6.--Three coil galvanometer.
7.--Thermo galvanometer.
8.--Siemens's universal galvanometer.
9.--A shunt.
10.--Commutator.
11.--Rheostat.
12.--Resistance coils.
13.--Wheatstone's balance.
Electrometers indicate the presence of a statical charge of
electricity, by showing the force of attraction or repulsion between
two conducting bodies placed near together. This force depending in the
first place on the quantity of electricity with which the conducting
bodies are charged, ultimately depends on the difference of potential
between them; an electrometer is therefore strictly an instrument for
measuring difference of potential.[J]
Sir William Thomson's quadrant electrometer is the most perfect form
of electrometer yet constructed, and the one usually employed in cable
testing. It consists of a very thin flat aluminium needle spread out
into two wings, and hung by a wire from an insulated stem inside a
Leyden jar, which contains a cupful of strong sulphuric acid, the outer
surface of which forms the inner coating of the Leyden jar. A wire
stretched by a weight connects the aforesaid needle with this inner
coating. A mirror, rigidly attached to this needle by a rod, serves
to indicate the deflection of the needle by reflecting the image of
a flame on to a scale. The needle hangs inside four quadrants, which
are insulated by glass stems: each pair of opposite quadrants are in
electrical connection. Above and below the quadrants two tubes, at
the same potential as the needle, serve to screen it and the wires in
connection with it from all induction except that produced by the four
quadrants. Suppose the needle charged to a high negative potential (-),
then if the quadrants are symmetrically placed, it will deflect neither
to the right nor to the left, so long as the near quadrants are at the
same potential. If one of these be positive relatively to the other,
the end of the needle under them will be repelled from the negative
quadrant to the positive one, and at the same time the other end of the
needle will be repelled from in the opposite direction. This motion
will be indicated by the motion of the spot of light reflected by the
mirror, and the number of divisions which the spot of light traverses
on the scale measures in an arbitrary unit the difference of potential
between the + and - quadrants.