The Project Gutenberg eBook of Torpedoes and Torpedo Warfare, by C. W. Sleeman, Esq.

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.

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.

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.

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.

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:—

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.

The reflecting electrometer being a very delicate instrument, requires careful handling, and should only be used by a practised electrician. Its use would therefore be restricted to important stations, and special tests of a delicate nature.

Thomson's Reflecting Galvanometer.—A galvanometer is an instrument intended to detect the presence of a current and measure its magnitude.

The most sensitive galvanometer as yet constructed is the reflecting galvanometer of Sir William Thomson, a diagram of which is shown at Fig. 84.

A small piece of magnetised steel watch spring, 3/8ths of an inch long, is fastened with shellac on the back of a little round concave mirror, and of about the size of a fourpenny piece. This is suspended by a piece of unspun silk thread in the centre of a coil of many hundred turns of fine copper wire insulated with silk, and well protected between the turns with varnish. The two ends of the coils are soldered to terminal screws a, b, so that any conducting wire can be joined up to it as required. The little mirror hangs in the middle of its coil, with the magnet lying horizontally. By means of a lamp L placed behind the screen, the light of which passes through a slit M, and is thrown on the face of the mirror, a spot of light is reflected on the scale N.

When a current passes through the coil, the little magnet is deflected, and since the magnet is attached to the mirror, which is very light, both are deflected as forming one body, and the spot of light moves accordingly along the scale N.

A powerful steel magnet S is placed above the coil, and can be moved up or down, whereby the directive force of the earth may be increased or weakened. This magnet S is used to steady the spot of light, which otherwise would shake about, and there would be no certainty about the measurement. A second magnet T is placed perpendicular to the magnetic meridian, to adjust the zero of the instrument, i.e., to bring back the spot of light to a fiducial mark at the centre of the scale when no current is passing.

This instrument should only be used at important stations, and when special tests of a delicate nature are required to be applied.

Astatic Galvanometer.—An astatic galvanometer is that in connection with which an astatic needle is employed, by the use of which the sensitiveness of a galvanometer is greatly increased.

An astatic needle is a combination of magnetised needles with their poles turned opposite ways.

At Fig. 85 a diagram of such an instrument is shown. Two magnets D and C are joined, with the north pole of one over the south pole of the other, forming one suspended system. In the ordinary form of astatic galvanometer the needles D and C are about two inches long, and are each covered by a coil, these latter being so joined that the current must circulate in opposite directions round the two so as to deflect both magnets similarly. The deflection of the needles D and C is observed by means of a pointer or glass needle A, B, rigidly connected with the astatic system by a prolongation of the brass rod connecting the needles D and C. The coils are flat and of the shape indicated in Fig. 85, and are also made in two halves, placed side by side with just sufficient space between them to allow the rod to hang freely.

This form of galvanometer, though less delicate than the preceding one, is still a very sensitive one, and should only be applied in the case of fine and delicate tests.

Differential Galvanometer.—A differential galvanometer consists of a magnetic needle surrounded by two separate coils of equal length and material carefully insulated from each other and wound in opposite directions. In using it one circuit acts against the other. If a current of equal strength were passing through each there would be no deflection of the needle, because the influence in both directions is equal. If one current were stronger than the other, the needle would be deflected by the stronger.

This form of galvanometer will be found extremely useful in connection with a system of electrical tests.

Latimer Clark's double shunt differential galvanometer is the instrument best adapted for submarine mine tests.

Detector Galvanometer.—A detector galvanometer is usually made with a vertical needle, and is employed to detect and roughly estimate the strength of a current where no particular accuracy is required.

It consists of a magnetic needle pivoted in the centre of a coil of insulated wire, and having an index needle attached to move with it, the latter appearing on a dial, divided into 360 equal arcs or portions: a diagram of such an instrument is shown at Fig. 86.

This instrument should be of small size and portable form, and as sensitive as it is possible to make it, under such conditions.

Three Coil Galvanometer.—The three coil galvanometer is provided with a vertical needle, and is in other respects very similar in appearance to the detector galvanometer before described. It is formed with three coils of 2, 10, and 1000 ohms resistance; each coil is connected with a brass plate on the top of the box which encloses the whole, and may be switched into circuit by means of a plug at will. The object of the three resistances is to suit the different resistances that may occur, with a perfect, or imperfect state of the electrical combination in connection with each mine. A diagram of this instrument is shown at Fig. 87, the dotted portions are inside the case.

Thermo Galvanometer.—A thermo galvanometer is an instrument used to ascertain the power of a firing battery which is employed to ignite platinum wire or low tension fuzes.

The form of thermo galvanometer generally used in connection with a test table, is arranged as follows:—

Two ebonite studs, fitted with brass connecting screws, are fixed to the lid of a box containing some resistance coils, and placed in circuit with them; these studs, placed about ·3 of an inch apart, are arranged to receive a piece of platinum wire which is stretched from one stud to the other; the firing battery being placed in circuit with the platinum wire, and the resistance coils, its working power would then be tested by the fusion of the wire through a given electrical resistance, as indicated by the resistance coils put in circuit.

Another form of thermo galvanometer, which is very compact and portable, is shown at Fig. 88. It consists of a wooden box a, with a cover of ebonite b, within the box is placed a resistance coil c; d and e are two ebonite standards ·3" apart, the former of which is connected by a copper wire with the terminal f, the latter to the terminal g; the terminal h is similarly connected to the contact piece k, and the terminal l to the firing key m, at n; the resistance coil c is connected to the terminal g and to the copper wire n; the platinum wire (of which several lengths are used, according to the resistance of the coil c) is placed between the standards d and e. To test a battery, it is only necessary to connect it to the terminals f and h, when by pressing down the key m the power of the battery, according as to its fusing or not the platinum wires, will be ascertained; the use of the terminals g and l is to cut out the resistance, which is effected by connecting them by means of a copper wire.

Siemens's Universal Galvanometer.—Siemens's universal galvanometer is an instrument combining in itself all the arrangements necessary for the following operations:—

The instrument which is shown in elevation and plan at Pl. xxiii., Fig. 1 and 2 respectively, consists of a sensitive galvanometer which can be turned in a horizontal plane, combined with a resistance bridge (the wire of which bridge instead of being straight is stretched round part of a circle). The galvanometer has an astatic needle, suspended by a cocoon fibre, and a flat bobbin frame wound with fine wire. The needle swings above a cardboard dial divided in degrees; as however, when using the instrument the deflection of the needle is never read off, but the needle instead always brought to zero, two ivory limiting pins are placed at about 20 degrees on each side of zero.

The galvanometer is fixed on a graduated slate disc, round which the platinum wire is stretched. Underneath the slate disc three resistance coils of the value of 10, 100, and 1000 Siemens' units are wound on a hollow wooden block, which protrudes at one side, and on the projection carries the terminals for the reception of the leading wires from the battery and unknown resistance. The adoption of three different resistance coils enables the measuring of large as well as small resistances with sufficient accuracy.

Slate is adopted for the material of which to make the disc f, because it is found by experience to be the material which is the least sensitive to variations in the weather or temperature.

The slate disc is graduated on its upper edge through an arc of 300 degrees, zero being in the centre, and the graduations figured up to 150 on each side at the terminals l and l¹ of the bridge wire.

In the centre of the circular plate E of polished wood, supported upon three levelling screws b, b, b, a metal boss is inserted, in which turns the vertical pin a which carries the instrument. This pin, being well fitted to the boss, supports the instrument firmly, but at the same time allows it to be turned freely round its vertical axis without losing its horizontal position when once obtained.

On the arm D D, which turns on the pin a, and somewhat behind the handle g, there is a small upright brass arm d turning between two screw points r, and carrying in a gap at its upper end a small platinum jockey pulley e turning on a vertical axis. This pulley forms the movable contact point along the bridge wire, against which it is kept firmly pressed by means of a spring acting on the arm d. The arm D D, which is insulated from the other parts of the apparatus, is permanently connected with the terminal I. On the top of d a pointer Z or a vernier is fixed, which laps over the upper edge of the slate disc and points to the graduations.

To the pin a is attached a circular disc of polished wood C, about one inch thick, and having a groove turned in its edge for the reception of the insulated wires composing the resistances. The disc C has a projection c, which carries the five insulated terminals marked I., II., III., IV., V., as shown on Fig. 1 and 2, Pl. xxiii. Terminals III. and IV. can be connected by a plug, II. and V. by the contact key K. Terminal I. is in connection with the lever D D.

Fig. 3 and 4, Pl. xxiii. show the shunt box supplied with the galvanometer if specially desired; the copper connecting arms a, a are screwed to the terminals II. and IV. By inserting a plug at c (Fig. 4, Pl. xxiii.), the galvanometer is put out of circuit altogether, whilst by plugging either of the other holes shunts of the value of 1/9, 1/99, or 1/999, are introduced into the circuit, and the effect upon the galvanometer is reduced to 1/10, 1/100, 1/1000, respectively of what it would have been without the insertion of the shunt.

Fig. 5 and 6, Pl. xxiii., show a battery commutator allowing to bring into the circuit four different amounts of battery power. It is placed in the battery circuit whenever consecutive tests with different batteries are desired to be made, it being only necessary to change the place of the stopper in the battery commutator, the terminal screw a of the battery commutator being connected to terminal V. of the galvanometer, and the screws b, b, b, b to various sections of the battery: see diagram of connections, Fig. 4, Pl. xxiv.

The application of the universal galvanometer will be clear from the diagrams on Pl ii.; instructions, however, for its practical use are added further on, and also tables for use when measuring conducting resistances.

As will be seen from diagram, Fig. 1, Pl. xxiv., the proportion between the unknown resistance X, and the artificial resistance n is, when the deflection is read off on the side of the slate disc marked A:

	X	: n	=	150 + a	: 150 - a
or,	X		=	150 + a	· n.
or,	X			150 - a	· n.

The values of these two fractions, for every half degree, will be found in the columns headed A and B of the table in the Appendix.

a.—The needle i is to be brought to the zero point of the small cardboard scale by turning the galvanometer G round its vertical axis, taking care that the needle moves with perfect freedom.

b.—The pointer or vernier Z is to be brought, by means of the handle g, to the zero point of the large scale on the slate disc.

c.—A plug is to be inserted between the terminals marked III. and IV.

d.—The holes 10, 100, and 1000 are, two of them, to be plugged, and one left open, according to the extent of the unknown resistance to be measured; either 10 or 100 must be left open if the resistance is small, and 1000 if it is large.

e.—The two ends of the unknown resistance are to be connected to terminals II. and IV.

f.—The two poles of some galvanic battery are to be connected to terminals I. and V.

When the above-mentioned connections have been made, and on depressing the key K, the battery current is sent into the combination and deflects the needle, say, to the right-hand or B side of the instrument, the pointer or vernier Z must then be pushed, by means of the handle g, to the B side of the instrument. If this is found to increase the deflection of the needle i, the pointer Z should be pushed to the other or A side of the instrument beyond the zero point of the large scale until the needle remains stationary when the key K is depressed.

The number indicated by the vernier Z should be read off carefully, and notice taken whether it is on the A or B side of the large scale. This number must then be referred to the galvanometer table,[K] when the figure opposite to the number, multiplied by the resistance unplugged, is the resistance of X. The value of the resistance to be determined will be thus found by a single operation.

Supposing the reading to be 50 on the A side of the large scale, the resistance n unplugged having been 100 units, we get according to the before-mentioned law of resistance bridge the following proportion (see Fig. 5, Pl. xxiiiA.):—

X :	100	=	150 + 50	: 150 - 50
	X		150 + 50	× 100
			150 - 50
	X	=	200 units.

For measuring very small resistances a single cell will be found sufficient; but for large resistances more should be used, say, 15 to 20. If very accurate measurements of small resistances are to be taken, the screw at the end of the moving arm D D should receive one battery wire, terminal V. receiving the other.

Comparing Electromotive Forces.—For this purpose Professor E. du Bois-Reymond's modification of Poggendorff's compensation method is used.

For comparing two electromotive forces E₁ and E₂, a third electromotor of higher electromotive force E₀ is used, and two separate tests taken.

c.—The hole between III. and IV. to be left unplugged.

d.—Plugs to be inserted in 10, 100 and 1000.

e.—The two poles of the electromotor of an electromotive force E₀ are to be connected to the terminals III. and V.

f.—The poles of the battery whose electromotive force E₁ is to be compared are connected to terminals I. and IV. in such a manner that the similar poles of the two electromotors are joined to terminals I. and III., and to IV. and V. respectively.

When depressing the key K the galvanometer needle will be deflected and can be brought back to zero by turning the pointer Z either to the right or to the left. Should for instance the pointer have to be brought to 30° on the A side we have the following equation—