Chapter IV: DEFENSIVE TORPEDO WARFARE--continued (1)

_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like a practicable form of self-acting apparatus; but within the last few years, the former has almost entirely superseded the latter method, except in very exceptional cases; this revolution being due to the vast improvements that have been, and still are being effected in the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.

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.

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}.

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.

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.

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.

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.

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.