4th Experiment.
Countermine:—As before, but moored 29-1/4' below the surface.
Effect of explosion:—(a) mine, at 195' distance, completely stove in; (c) mine, at 58' distance, case indented but charge dry; (e) mine, at 175' distance, slightly leaky; (f) mine, at 48-1/2' distance, upper half indented in three places. It was also discovered during the above experiments that submarine mines charged with dynamite can be caused to explode by the detonation of a charge of the same explosive, at distances from it considerably beyond those at which the cases themselves are damaged by a similar charge. To prevent the foregoing, it is necessary to pack the dynamite very carefully, using at the same time special precautions.
CHAPTER X.
THE ELECTRIC LIGHT—TORPEDO GUNS—DIVING.
ELECTRIC lights combined with fast steam launches as guard boats and specially constructed torpedo guns, such as the Nordenfelt and Hotchkiss machine guns, are at the present time the only truly practicable means afforded to a man-of-war of defending herself against the attack of torpedo boats, whether these latter are armed with the spar, fish, or towing torpedo; the torpedo gun sinking the boats after the electric light and guard boats have detected their approach and position.
As has been before stated, nets, shields, booms, &c., placed around a vessel of war, must, however slightly constructed, affect to a considerable degree her efficiency, by decreasing her power of moving quickly in any desired direction, which is essential to the utility of such a vessel in time of war; and thus on electric lights, guard boats, and torpedo guns must the safety of ships in future wars really depend, when attacked by torpedo boats.
The Electric Light.—The phenomenon of the Voltaic arc was first discovered by Sir Humphry, then Mr., Davy at the beginning of the present century. The following is an account of the matter as given by him in his "Elements of Chemical Philosophy":—
"The most powerful combination that exists, in which number of alternations is combined with extent of surface, is that constructed by the subscription of a few zealous cultivators and patrons of science in the laboratory of the Royal Institution. It consists of 200 instruments, connected together in regular order, each composed of ten double plates arranged in cells of porcelain, and containing in each plate thirty-two square inches; so that the whole number of double plates is 2,000, and the whole surface 128,000 square inches. This battery, when the cells were filled with sixty parts of water, mixed with one part of nitric acid, and one part of sulphuric acid, afforded a series of brilliant and impressive effects. When pieces of charcoal about an inch long and one-sixth of an inch in diameter were brought near each other (within the thirtieth or fortieth part of an inch), a bright spark was produced, and more than half the volume of the charcoal became ignited to whiteness, and by withdrawing the points from each other, a constant discharge took place through the heated air, in a space equal at least to four inches; producing a most brilliant ascending arch of light, broad, and conical in form in the middle. When any substance was introduced into this arch, it instantly became ignited. Platina melted as readily in it as wax in the flame of a common candle; quartz, the sapphire, magnesia, lime, all entered into fusion; fragments of diamond, and points of charcoal and plumbago, rapidly disappeared, and seemed to evaporate in it, even when the connection was made in a receiver exhausted by the air pump; but there was no evidence of their having previously undergone fusion."
The philosopher also showed that, when the Voltaic or electric arc is produced in the exhausted receiver of an air pump, the phenomena are as brilliant in character, and the charcoal points can be more widely separated, thus proving that the electric light is quite independent of the oxygen of the air for its support.
Owing to the crude nature of the Voltaic batteries of that day, and also to the great expense of maintaining a large battery of that nature, nothing practical resulted from Davy's discovery of the electric or Voltaic arc. Professor Faraday, the great physicist, by his discovery of the principle of magneto-electricity, has enabled the electric light to be brought into practical use. As early as 1833 Pixii applied the principle practically in the construction of a magneto-electric machine with revolving magnets; he was followed by Laxton, Clark, Nollet, Holmes, and others, who made machines with fixed magnets. In 1854 Dr. Werner Siemens, of Berlin, introduced the "Siemens' Armature," which, from its compact form, permitted a very high velocity of rotation in an intense magnetic field, giving powerful alternating currents, which, when required, were commutated into one direction.
The latest improvement has been that from the magneto-electric to the dynamo-electric machine. It is due to both Dr. Siemens and Sir C. Wheatstone. Induced currents are directed through the coils of the electro-magnets which produce them, increasing their magnetic intensity, which in its turn strengthens the induced currents, and so on, accumulating by mutual action until a limit is reached.
Siemens' Electric Light.—The following is a description of Messrs. Siemens Brothers' dynamo-electric light apparatus, which, for use on board ship against boat torpedo attacks, &c., is equal, if not superior, to any similar apparatus yet produced, and which is extensively used in the German and other European navies. This apparatus was one of many others experimented on by Dr. Tyndal and Mr. Douglas, M.I.C.E., for the Trinity House.
Dr. Tyndal says: "I entirely concur in the recommendation of Mr. Douglas, that the Siemens machine recently tried at the South Foreland be adopted for the Lizard. From the first I regarded the performance of this handy little instrument as wonderful. It is simple in principle, and so moderate in cost that a reserve of power can always be maintained without much outlay. By coupling two such machines together, a great augmentation of the light is moreover obtainable."
Principle.—When a closed electrical circuit is moved in the neighbourhood of a magnetic pole, so as to cut the lines of magnetic force, a current is generated in the circuit, the direction of which depends upon whether the magnetic pole is N or S; it also depends on the direction of motion of the circuit, and according to the law of Lenz, the current generated is always such as to oppose the motion of the closed circuit.
All magneto-electric and dynamo-electric machines are based on the principle stated above, and are subject to many modifications.
The name dynamo-electric machine is given to it, because the electric current is not induced by a permanent magnet, but is accumulated by the mutual action of electro-magnets and a revolving wire cylinder or armature. It is found that, as the dynamic force required to drive the machine increases, so also does the electric current; it is therefore called a dynamo-electric machine.
Description.—In the machine here described, of which [Fig. 164] is an elevation, [Fig. 173] a part elevation, and [Fig. 165] a longitudinal section, the electric current is produced by the rotation of an insulated conductor of copper wire or armature coiled in several lengths, 8, 12, 16, &c., up to 28, and in several layers, longitudinally, upon a cylinder with a stationary iron core nn' ss', so that the whole surface of the armature is covered with longitudinal wires and closed at both ends, as in [Fig. 165]. This revolving armature is enclosed to the extent of two-thirds of its cylindrical surface by curved soft iron bars NN1, SS1.
The curved bars are the prolongations of the cores of the electro-magnets E E E E. They are held firmly together by screws to the sides or bottom of the cast iron frame of the machine, making it compact and strong.
The coils of the electro-magnet form with the wires of the revolving armature one continuous electric circuit, and, when the armature is caused to rotate, an electric current (which at first is very feeble) is induced by the remanent magnetism in the soft iron bars and directed through the collecting brushes into the electro-magnet coils, thus strengthening the magnetism of the iron bars,[V] which again induce a still more powerful current in the revolving armature.
The electric current thus becomes stronger and stronger, and the armature therefore revolves in a magnetic field of the highest intensity, the limit of which is governed by the limit of saturation of the soft iron.
At each revolution the maximum magnetic effect upon each convolution of the armature is produced just after it passes through the middle of both magnetic fields, which are in a vertical plane passing through the axis of the machine (i. e. N1S1 in Fig. 173). The minimum effect is produced when in a plane at right angles to it, i. e. horizontal.
According to the law of Lenz already referred to, when a circuit starts from a neutral position on one side of an axis towards the pole of a magnet, it has a direct current induced in it, and the other part of the circuit which approaches the opposite pole of the magnet has an inverse current induced in it; these two induced currents are, however, in the same direction as regards circuit. A similar current will also be induced in all the convolutions of wire in succession as they approach the poles of the magnets.
These currents, almost as soon as they are induced, are collected by terminal rollers or brushes B, usually the latter, placed in contact with the commutator in the position which gives the strongest current. The position giving the strongest current gives also the least spark, so that when there are no sparks at the commutator the best lighting effect is produced. [Fig. 166] shows position of brushes when the armature revolves in the direction indicated by the arrow.
The circumference of the revolving armature is divided into an even number of equal parts, each opposite pair being filled with convolutions of insulated wire wound parallel to the axis of the armature.
The ends of these wires are brought to a commutator and connected to the segments either by screws or by soldering.
The brushes collect the electric currents as they are induced, which is nearly constant and continuous.
The collecting brushes are combs of copper wire placed tangentially to the cylindrical commutator, and press lightly upon it with an elastic pressure.
Power and Light produced.—An increase of the armature speed produces a corresponding increase in the current produced, but not in the same proportion. The current increases more rapidly than the speed, and could be made to reach any intensity but for considerations explained below. With increase of current there is also increase of heat.
The speed for continuous work must not be taken too high, because the heat developed at high velocities might destroy the insulation of the coils of the electro-magnet. The speed given for this machine produces no such injurious heating effect.
The strength of the current is also influenced by the resistance of the electric lamp and its leading wires. With an electric lamp in a circuit of proper resistance the armature should revolve at the rate given in the following Table. The heating will then reach its maximum, which is very moderate, in about three hours after which there will be no further change.
Table.
| Size. | Number of revolutions of armature. | Intensity of light in standard candles. | HP (actual) to drive. |
| Medium | 800 to 850 | 4,000 to 6,000 | 3½ to 4 |
The intensity of the unassisted light is given in standard candles. The standard here used is a stearine candle consuming 10 grammes per hour.
Regulation.—From the fact that a closed circuit rotating in a magnetic field experiences resistance to its motion which a broken circuit does not, motive power to any extent is only required when the circuit is closed. An interruption of the current is therefore equivalent to removing the load from the motor, which for mechanical reasons may be injurious to it and for electrical reasons to the dynamo machine.
The sudden interruption of the circuit of the large machine produces an electric tension so dangerously high as to strain or destroy the insulation of the machine. When contact is again made after such interruption, the increase of speed resulting from the interruption causes a momentary current of great intensity, accompanied by sparks at the commutator.
In order that the light may be quite steady the speed should be as uniform as possible. As too high an increase of speed may result in temporary extinction of the light, it ought never to be permitted. The motor should therefore be provided with a good and sensitive governor, that will keep the speed perfectly uniform however the steam and load may vary. A large and heavy fly-wheel is also very useful in keeping the speed nearly uniform during change of load.
Although the circuit, when the machine is in full action, should never be suddenly interrupted, interruption arising from the extinction of the light is not dangerous, because it is always preceded by a decrease in the strength of the current. When it is desired to divert the current into another circuit it is advisable to stop the machine. Although in practice with small machines this is rarely done, with large machines it is necessary.
Self-acting Shunt.—For great security, especially with the two machines coupled together, where the electric current is strong and the light equivalent to about 14,000 candles, it is advisable to insert in the circuit a self-acting shunt.
This is placed between the lamp and machine and connected to both leading wires. Its principle is as follows:—
The terminal M, [Fig. 167], is joined by a short connecting wire to one terminal of the machine. The terminal L M is connected to the remaining terminal of the machine and also to one of the lamp terminals.
The terminal L is connected to the other terminal of the lamp.
The shunt contains a small electro-magnet E mounted upon a square wooden slab or baseboard with its armature a, a contact c, and, below the slab, a resistance coil W, which is equal to the resistance of the electric arc of the light, about 1 S. u.[W]
As long as the lamp is burning well, the current circulates in the coils of the electro-magnet, and the armature a being strongly attracted, there is no contact at c. The resistance coil W is therefore not in electrical circuit. When the light is extinguished the current in the coils of the electro-magnet ceases, and the armature is withdrawn by the spring f making contact at c. This offers to the electric current a path through W of equal resistance to that of the lamp, and the current is subjected to scarcely any change, so that the motor has practically no cause to alter its rate.
When the carbon points of the lamp again touch, the electric current returns to them, breaking contact at c, re-establishing the former conditions.
Direction of Rotation.—The armature may revolve in either direction. If it becomes necessary to drive it in the opposite direction to that for which the machine has been made, it is only necessary to reverse the brushes, placing their points in the direction of motion, and to change two of the wire connections, which operations can be effected in a few minutes. [Fig. 166] shows the position of brushes for one direction of rotation and [Fig. 168] that for the other.
Conducting or Leading Wires.—The leading wires are usually of copper of high electrical conductivity. They must be insulated from one another the whole of their length and not placed too close together. As their resistance affects the intensity of the light very much, the section must be carefully proportioned to the distance of the lamp from the machine.
The best practical result is obtained when their resistance together with that of the lamp is equal to the total internal resistance of the dynamo machine. Wires of various sizes are therefore required.
Decrease in strength of the current caused by a leading wire of too high resistance can be overcome by a higher velocity, which is obtained only by increased motive power, but if the wire is much too small, it will become heated. The proper remedy is to increase the sectional area of the leading wire.
Bright sparks should never be allowed to appear at the commutator and brushes, as sparks result from a rapid burning of the metallic parts. They can easily be avoided by properly inclining the two arms which carry the brushes.
The position of the brushes yielding the least spark at the commutator is that giving the highest intensity of light in the electric arc.
The commutator should, while in motion, be freely oiled, to prevent the brushes wearing away too rapidly. The sticky oil should from time to time be removed by washing with paraffine oil or benzoline.
Wear and Tear.—The chances of stoppage so common to the old forms of electric light apparatus have in this form been reduced to a minimum, and now do not exceed those that arise with machines generally. The Trinity House Report states that the Siemens' machine worked well for a month without any necessity for stopping. The brushes are the only parts which wear away, and they are very easily replaced.
In thick weather they should be connected in what is called parallel circuit (or parallel arc, or for "quantity"), because it has been found that when they are so arranged the intensity of the electric light produced exceeds by some twenty per cent. the intensity of the sum of the two when worked separately. Thus the two machines, giving respectively a candle power of 4,446 and 6,563 when worked separately (total 11,009), have given when coupled up in parallel circuit a light equivalent to 13,179 candles; just as in telegraphy it has been found that the rate of sending can be increased from 20 to 25 per cent. when the apparatus is coupled up in parallel arc. For this reason it is usual to employ two machines of medium size instead of one machine of large size. The intense light so produced is also much more uniform than from one large machine.
Automatic Electric Lamp.—Automatic electric lamps have been constructed with spring clockwork to cause the carbons to approach one another to a certain point, when, by means of an electro-magnet, the clockwork is checked, and the carbon points are allowed to burn away to such a distance that, by the decrease of current, the clockwork is released and the carbons caused to approach again. With such lamps the clockwork has been a source of trouble, and it is liable to get out of order.
Siemens' Patent Electric Lamp.—The lamp here described is actuated without clockwork; it also automatically separates the carbons after they have approached too closely or touch, and, by this combined action of approaching and separating, the carbon points are kept at a proper distance apart, and a steady light is obtained.
The working parts are represented in the diagram [Fig. 169], and at [Fig. 170] is shown the size employed on board ship.
E is the horse-shoe magnet with the armature A placed in front of its poles a short distance from them. A regulating screw b with the spiral spring f is attached to the lever A', forcing it against the stop d, and withdrawing the armature from the poles of the electro-magnet. When a current traverses the coils of the latter of sufficient strength to attract the armature and overcome the tension of the spring f, contact is made at c, which diverts the current from those coils. The consequent release of the armature breaks contact at c, the armature is again attracted, and this action is repeated, producing a vibrating motion of the lever and armature, which continues as long as there is sufficient current to overcome the tension of the spring.
The spring pawl s at the upper end of the lever A', and oscillating with it, actuates a ratchet-wheel u, which is in gear with a train of wheels and the carbon holders; it thus opposes their tendency to approach by pushing them apart, tooth by tooth, until the current is so much weakened by the increased length of electric arc that the armature and lever cease to oscillate enough to move the teeth of the ratchet-wheel, and it rests near the stop d.
While in this position the spring pawl is released from the ratchet-wheel and the preponderating weight of the upper carbon holder causes the carbon points to approach again. Increase of current follows decrease of resistance, the armature again oscillates, and this cycle of action is continuously repeated.
When in action the movements of the carbons are scarcely perceptible, but when, by any external cause, the carbons are separated so as to extinguish the light, they immediately run together until they touch, when they ignite and separate to a proper working distance by means of the electro-magnet above described.
The only operation requiring attention in the use of this lamp is the adjustment of the tension of the spring f. When this tension is once regulated to the current at disposal, the lamp will continue to give a steady light as long as the current remains uniform.
The relative rate of consumption of the two carbon points differs. The positive carbon burns away rather more than twice as quickly as the negative carbon.
The duration of the light depends mainly on the lengths and sizes of the carbons.
Provision is made in this lamp that the rack which supports the negative carbon may be made to gear either into the teeth of the same pinion as that of the positive carbon, or into one of about half the size. By these means the light, when once focussed in a reflector, will remain in focus as long as the carbons last, whether permanent or reversed currents are employed.
Besides its twofold application, the lamp is very compact, is simple in construction, and therefore not likely to get out of order, and it is capable of being regulated with great precision.
There is no spring to be wound up. The contact need not be cleaned, as the sparks are scarcely perceptible.
By removing two screws in the outside casing, all the chief working parts can be easily removed and inspected.
Carbons are made from the hard carbon deposited in the interior of gas retorts, also from graphite. Various sizes, both square and round in section, of from 5 to 20 mm. in diameter, are used in the electric lamp according to the intensity of the electric current. Those commonly employed are from 10 to 12 mm. in diameter.
The carbons supplied with the Siemens patent lamp are coated with a thin film of copper. This enhances the cost somewhat, but it greatly improves the result, as the carbons burn longer, and do not split, when so coated.
By coating them the resistance is diminished, except at the points, so that all the heat is concentrated in the electric arc, and a brighter light is the result.
When two dynamo machines are coupled together (see [page 248]), to give a very powerful current, the sizes up to 20 mm. are required.
The consumption varies a little, but the average is from 3 to 4 inches per hour.
Concentration of Light.—Two kinds of concentrating apparatus are supplied in combination with the automatic lamp, both of which are capable of giving a powerful parallel beam, which will reach to an enormous distance, and are well adapted for naval purposes. The one kind consists of a parabolic reflector of stout metal, its concave surface being silvered and burnished. The apparatus is mounted with a ball-and-socket joint upon a wooden stand, as shown in [Fig. 171].
The other kind is the Fresnel catadioptric lens or holophote, [Fig. 172], which may be substituted for the reflector, and gives a more powerful beam than one given by reflection. The lens is surrounded by a metal case or lantern, in which is placed the electric lamp upon a slide for focussing. Behind the carbon points a hemispherical reflector is placed, to catch all the back rays, and reflect them back through the lamp focus. The entire lantern is capable of revolving on horizontal rollers, and swings upon pivots. Two handles are placed at the back to manipulate it.
As the electric arc is much too bright to be looked into with the naked eye, both concentrating apparatus are supplied with a lens, called a focus or flame observer, by means of which an image of the burning carbons is thrown upon small screens at the back, so that the lamp can be easily adjusted without fatigue to the eye. The focus observer is shown on the lamp in holophote, [Fig. 172].
Precautions.—Before starting the apparatus, the electric lamp terminals and those of the dynamo machine must be connected up by means of the leading wires provided with each set of apparatus. The terminals are marked C and Z respectively, and they should be connected, C of machine to C of the lamp, and Z of the machine to Z of the lamp, in order that the electric current may be sent in the proper direction through the carbons of the lamp. Should it, however, be found that the top carbon (which should consume twice as fast as that of the bottom one) does not consume so fast as the bottom one, it may be assumed that the dynamo machine has reversed its poles, and the leading wires will consequently require changing across. This reversal of poles, though possible, is of very rare occurrence.
The dynamo-electric machine should not be driven without its proper leading wires to lamp and lamp being connected up, or at least an external resistance equivalent to that of the lamp (which is approximately one Siemens' unit) must be inserted. In other words, the machine must not be driven when a wire of small resistance connects the two terminals C and Z. This is expressed more briefly by saying the machine must not be short-circuited. If it is short-circuited when in motion the electric current becomes so powerful that it will leap from segment to segment of the commutator, where very bright and large sparks will be seen, and if continued would destroy the insulation, thus weakening the current generated.
The leading wires should never be disconnected suddenly while the machine is revolving at its full speed, as such a sudden interruption will produce an intense spark, which will burn the ends of the wire where the contact is suddenly broken. When it becomes necessary to disconnect the wires, the belt should be pushed on to the loose pulley by means of the striking gear, or the steam engine should be stopped.
It may be here stated that all connections should be cleaned bright and screwed tightly, to ensure perfect metallic contacts being made.
Coupling two Machines.—At [Fig. 174] is shown a diagram of how to make the connections when coupling two machines in parallel circuit. MM', m, m', represent the ends of the wires of the electro-magnets; BB' are the branches; C and Z are the terminals of each machine respectively.
The three ways in which the various wire connections of these machines are joined up, and which are enough for all ordinary purposes, are given below in paragraphs (a), (b), and (c).
(a) When the machine is working singly and revolving in the direction indicated in [Fig. 166], the following connections are made:—
| M | is connected with | B, |
| M' | " | B', |
| m | " | Z, |
| m' | " | C, |
and the leading wires of the lamp are connected with C and with Z as explained.
(b) When working singly and revolving in the direction indicated in Fig. 168:—
| M | is connected to | B', |
| M' | " | B, |
| m | " | Z, |
| m' | " | C. |
Thus the only change necessary when the machine is to be driven in the opposite direction to that for which it is made, is to disconnect at B the wire from M to B and at B' the wire from M' to B', and to cross them. The machine will then be connected as above (b).
(c) When working two machines in parallel circuit, as in [Fig. 174], they must be connected as follows (that on the left of the page being called the first machine, and that on the right the second machine):—
| C | of first to | C | of the second. |
| Z | " | Z | " |
| M | " | B | " |
| B | " | M | " |
| M' | " | B' | " |
| B' | " | M' | " |
and then connect C and Z of the second machine with the leading wires of the lamp.
The connections m to Z and m' to C in each machine are the same as in cases (a) and (b). They do not require to be altered, and may therefore be left out of consideration in all three cases (a), (b), and (c). The whole of the connections here indicated can be quickly made by means of a cross-bar commutator or switch, which is supplied with the machines in cases where such changes are likely to be required frequently. This is usually attached to a wall, leading wires being taken to it from the dynamo machines separately, and others from the switch being led to the electric lamps.
The leading wires from machine to lamp should, whenever possible, be kept separate, to prevent them rubbing together and making contact. A distance of two inches is quite sufficient to prevent accidents of any kind.
When the leading wires are erected in places where they are likely to rub and chafe against hard substances, it is advisable to enclose each wire separately in india-rubber tubing at all the points where they are likely to be rubbed. This becomes very important on board ship, where everything is in motion, and special care is in consequence required.
Some dynamo machines are coupled direct to the crank shaft of the steam engines; they require the same kind of attention as others, that is to say, they should be driven at a uniform speed, should be well oiled as well as the steam-engine, and they should be kept clean and free from sharp grit.
Application.—The electric light used in the case of a direct attack by torpedo boats, without the assistance of guard boats, will not prove of much assistance, on account of the very small space covered by the beam of light, and therefore if the direction of attack is not exactly known, the beam of light must be kept continually sweeping round the horizon on the chance of picking out the attacking boats, and thus, while flashing in one direction, they may be approaching in another, and effect their deadly mission.
Every man-of-war should be fitted with at least three electric lights, whereby the above-mentioned want of space covered would be to a considerable degree obviated.
If a powerful beam of light be thrown in a particular direction, and there kept stationary, all boats or vessels crossing its path at a distance not exceeding 1600 yards from the ship using the electric light, would become distinctly visible to observers placed behind the light; these vessels remaining visible as long as they continue in such a position that the beam of light acts as a background to them. Under very favourable circumstances, the distance at which the above effect may be observed is much increased.
The parabolic reflector extends only about an arc of 33° at 540 yards' distance from the light.
One defect of this form of reflector is, that it is rapidly dimmed by spray, rain, and by the particles given off by the carbons.
The catadioptric lens, or holophote, gives a far more powerful but a more concentrated beam than the parabolic reflector. By means of such a beam of light, a torpedo boat may be discerned at about one mile distance. By adding divergent lens to the holophote, a less powerful and less concentrated beam of light will be thrown out; in this case about 20° of surrounding water would be well illuminated at about 900 yards' distance, while without the divergent lens there would be only about 5° so illuminated but far more brilliantly.
The distance at which objects can be detected by the electric light depends on their size and colour, more particularly on the latter.
The observer should as a rule be well removed from the light.
In the case of an electric light being thrown on the observer, the vessel, &c., using it would to that observer be invisible, the light only being seen; also when directed on any particular object, surrounding objects would be thrown into shade.
The electric light will be found very useful for signal purposes by fitting a plane mirror in front of the catadioptric lens; so arranged that it be turned to any desired angle to the axis of the beam of light. By altering the angle of the mirror, the reflected beam of light can be swept from the horizon on one side, through the zenith, to the horizon on the other side. The time of passing the zenith being equivalent to the long and short flashes of the usual night signal code.
In addition to using the electric light to detect the approach of torpedo boats, it may be used by the boats themselves to prevent the attacked vessel from discerning them.
In turret ships, electric lights may be so arranged that the instant an object is brought into the field of the beam of light, the turret guns will be bearing on it.
One great disadvantage of electric lights is the impossibility of protecting them from the enemy's fire, and this is a defect that cannot be eradicated, though it may be lessened, by manipulating them from the tops of a ship.
Torpedo Guns.—Hitherto by torpedo guns has been meant small guns mounted on carriages so constructed that a shot may be fired into the water only a few feet from the ship's side, or mitrailleuses, Gatlings, &c. Here the term is applied only to machine guns, which are constructed to fire either volleys, or, extremely rapidly, single shot, each shot of which would be capable of penetrating and sinking torpedo boats, such as Messrs. Yarrow and Thornycroft are daily launching from their yards. Of such weapons there are at present only two, viz., the "Nordenfelt" and "Hotchkiss" gun. The former has, after very exhaustive experiments, been adopted by the English, Austrian, Swedish, and other naval authorities, while the latter has been adopted by the French government.
Nordenfelt Torpedo Gun.—This gun, as it at present is constructed, consists of four barrels of 1 inch calibre.
The barrels are fixed in a horizontal plane, and are not moved during the firing; and the movement of the lever, the loading, the firing, and the extracting are all performed in the same plane, so that the elevation of the gun is not disturbed by the firing.
The gun is fed by means of hoppers, each of which contains ten rounds per barrel, i. e., forty shots.
The continuous supply of cartridges, as well as the firing and extracting, are all performed by one motion of the lever, thus enabling the gunner to use his left hand to lay the gun.
A volley of four shots can be fired at the same moment, or one shot can be fired separately. Eight shots can be fired in 1-1/4 seconds; twenty, thirty, or forty shots can be fired at a rapidity of two hundred shots per minute without difficulty.
The recoil being taken up by the whole framework of the gun does not in the least disturb the aim.
The entire mechanism of the gun can be opened up without undoing a single screw, in less than 20 seconds.
All the four spiral firing springs can be taken out, without opening the rest of the mechanism, in 1-1/2 seconds.
All the parts of the mechanism are made interchangeable, so that reserved parts can at any time be substituted. The gun can be placed on half cock, so that the strikers do not act; and for further security the lever can be locked. The carrier block, without which the gun cannot be fired, is loose, and can be taken away, in case it becomes necessary to abandon a gun, which is thus made useless to the enemy.
The bullets are solid steel, weighing about 1/2 lb. At 1760 yards at right angles this gun will penetrate a 3/16 inch steel plate, which represents the thickness of the plates of a torpedo boat.
At 200 yards at right angles it will penetrate one 3/16 inch steel plate placed in front of a 1/2 inch steel plate with a space of 3 feet between them, this target representing the plates and boiler of a torpedo boat.
At the same distance, at 30° angle against the line of fire, it will penetrate a 1/2", 1/4", or 3/16" steel plate.
The holes in some instances are from 6 to 11 inches in length, and 2-1/2 inches in height. Angle of depression 20°, of elevation 30°, and of direction 360°.
Weight of the gun 3-3/4 cwt., and weight of carriage 2-1/2 cwt.
Hotchkiss Torpedo Gun.—This gun consists of a group of five barrels, revolving on a central shaft, a breech block, containing the firing mechanism, a feeding hopper, and the necessary hand crank for training and firing. The gun is mounted on trunnions attached to a vertical column, which rests in a suitable socket bolted to the ship's side; by this means a universal motion is obtained.
The essential difference between this and the Nordenfelt gun is, that the barrels and mechanism are put into rotatory motion.
Another point of difference is that single shots only can be fired, and not a volley, as in the Nordenfelt gun.
With the Hotchkiss gun, only some thirty shots can be fired in one minute at an advancing torpedo boat. The weight of the Hotchkiss steel shot is about 1 lb., but owing to the low velocity of the gun, its penetrative power is little more than that of the Nordenfelt 1/2 lb. bullet.
The object to be gained in firing at an attacking torpedo boat is to sink her, and not merely to kill or disable her crew, for supposing the attack to be made with a contact spar torpedo, and the boat to have reached within 300 yards' distance from the ship, then, even if all the crew (probably two or three men) were disabled or killed, the boat would, if not sunk, still carry out its work of destruction; therefore the projectiles to be used under such circumstances should be only those capable of penetrating a torpedo boat's plates, i. e., solid steel shot, not shells.
Diving.—In laying down and in picking up submarine mines, divers will be found extremely useful; also in clearing a passage in a river, &c., of an enemy's torpedoes in time of war. During the late Turco-Russian war, the harbour of Soukoum Kaleh taken by the Turks was popularly supposed to have been cleared of its mines by native divers (Lazees), but as the torpedoes so captured were never seen at Stamboul, it must have been a stretch of imagination; probably such would have been done, had there been any mines in the harbour to clear away.
The following is a general description of Messrs. Siebe and Gorman's improved diving apparatus.
The apparatus consists of
Air-pump.—This improved air-pump consists of two double action cylinders, each cylinder capable of supplying about 135 cubic inches per revolution. The advantage of this air-pump is, that it can supply air to two divers, working independently and at different levels, each diver being in direct connection with one of the cylinders. The air-pipes are in lengths of 45 feet and 30 feet, made of vulcanised india-rubber with a galvanised iron wire imbedded; this protects from corrosion, and allows the air to pass through the pipes with less friction.
Diving Dress.—The diving dress is made of solid sheet india-rubber, covered on both sides with tanned twill; it has a double collar, the inner one to pull up round the neck, and the outer one of vulcanised india-rubber to go over the breast-plate and form a water-tight joint. The cuffs are also of vulcanised india-rubber, and fit tightly round the wrist, making, when secured by the vulcanised india-rubber rings, a water-tight joint, at the same time leaving the diver's hand free.
Breast-plate.—The breast-plate is made of tinned copper, and has a valve in front, by which the diver can regulate the pressure of air inside his dress and helmet. The outer edge of the breast-plate is of brass, and is secured by screws to the outer collar of the dress.
Helmet.—The helmet is made of tinned copper, and has a segment bayonet screw at the neck, corresponding to that of the breast-plate, which enables the helmet to be removed from the breast-plate by one-eighth of a turn. It has three strong plate glasses in brass frames, protected by guards; two oval at sides, and a round one on the front; the front one can be unscrewed, to enable the diver to give and take orders. At the side is an outlet valve, which, by inserting a finger, the diver can close, and so rise to the surface. The valve allows the foul air to escape, and prevents the entrance of the water. An elbow tube is securely fitted on the helmet, to which is fixed an inlet valve, to which the air-pipe is attached. The inlet valve is made that the air can enter, but in case of a break in the air-pipe it cannot escape.
The front and back weights are of lead, heart-shaped, and weigh about 40 lbs. each.
Boots.—The boots are made of stout leather, with leaden soles, and are secured over the instep by a couple of buckles and straps. Each boot should weigh at least 20 lbs.
Crinoline.—The crinoline or shackle is used for deep water; it is placed round the body and tied in the front of the stomach: being supported by braces, it affords protection to the stomach, and enables the diver to breathe more freely.
Ladder.—An iron ladder should be provided with stays to bear against the side of the boat from which the diving is carried on, to which may be attached (if working in deep water) an ordinary rope ladder, with ash rounds, and weighted at the end. Some divers have the ladder only 20 feet long, to the last round a rope with a weight attached, which rests on the ground; by that means they descend.
Directions for using the Apparatus.—The ladder having been fixed, the position of the pump should be decided on, and it should be securely lashed by means of the ropes attached to the handles down to a stage, into which the screw-eyes should be fastened if necessary; the pump should be placed out of the way of the divers, the men attending on them, and all the men employed. The best position for the pump is facing the head of the ladder, and about six feet from it.
While the diver is dressing, the pump should be prepared for use, the winch handles should be taken out of the pump case, the nipples protecting the crank axles removed, the nuts being replaced on their screws. The nuts for the ends of the crank axles are taken off, the fly-wheel placed on the shaft, and the winch handles put on, and secured by the nuts, which are screwed home with the spanner. The pump is always worked in its case.
The flaps covering the pressure gauges and that at the back of the pump case should be opened, the screw on the overflowing nozzle of the cistern removed, and the cistern filled with water; the caps of the air delivery pipes should be removed, the necessary lengths of air-pipe should be put together carefully with washers in place, and all the screws must be worked home by means of the two double-ended spanners. The air-pipes should be tested by holding the palm of the hand to the end of the pipe, till the pressure shown on the pressure gauge is considerably above that corresponding to the depth the diver is to descend.
Dressing the Diver—Crinoline only for Deep Water.—The diver having taken off his own clothes, puts on a guernsey, a pair of drawers, very carefully adjusted outside the guernsey, and securely fastened by the tape round the waist, to prevent them from slipping down, and then a pair of inside stockings. If the water be cold, the diver may put on two or more of each of the above articles. He then puts on the crinoline and woollen cap, drawing the latter well over his ears; some divers find relief from putting cotton saturated with oil in their ears.
The shoulder pad is then put on, and tied under the diver's arms. He then gets into the diving-dress, which in cold weather should be slightly warmed, drawing it well up to his waist; he next puts his arms into the sleeves, an assistant opening the cuffs by means of the cuff expanders, or by inserting the first and second fingers of both hands, taking care to keep his fingers straight. The diver, by pushing, forces his hand through the cuff. He puts on a pair of outside stockings and a canvas overall to preserve the dress from injury.
The diver then sits down, and the inner collar of the dress is drawn well up and tied round the neck with a piece of spun yarn, and the breast-plate put on, great care being taken that the india-rubber of the outer collar is not torn in putting it over the projecting screws of the breast-plate. The four pieces of the breast-plate band, which with the thumbscrews had been previously placed for safety in one of the boots, are then put over the outer collar, and secured to the projecting screws by means of the thumbscrews; the centre screw of each plate should be tightened first. It will generally be sufficient if the thumbscrews be screwed up hand-tight, the spanner being only used when necessary. The canvas overall is now adjusted and the boots are put on.
The rings are passed over the cuffs, and the sleeves of the overall are drawn down to cover them. If gloves are to be used, the rings will be put on over them, as well as the cuffs. The helmet (without the front bull's-eye) is then put on; before doing so, the attendant should blow through the outlet valve of the helmet; he can do so by placing his head in the interior, and placing his mouth to the hole where the air escapes. Blow strongly; if in proper working order, the valve will vibrate. A loop of the life line is placed round the diver's waist, the line brought up in front of the man's body, and secured with a piece of small rope passing round his neck, or to the stud on the helmet. The waist-belt is buckled on with the knife on the left side, the end of the air-pipe being passed from the front, through the ring on the belt on the man's left, and up to the inlet valve on the helmet, to which it is secured; the upper part of the pipe is then made fast by a lashing to the stud on the left of the helmet. The diver then steps on the ladder, and two men are told off to man the pump.
The weights are then put on, the front weight first, the clips being placed over the studs on the breast-plate. The back weights are then put on, and the clip lashings over the hooks on the helmet, and the two are secured to the diver's body by means of the lashing from the back weight, which is passed round the waist, through the thimble beneath the front weight, and tied to the other end of the lashing at the back weight.
When the signalman is sure that all is right, and that the diver understands all the signals, he gives the word Pump, and screws the centre bull's-eye into the helmet securely; this done, he takes hold of the life line and "pats" the top of the helmet, which is the signal for the diver to descend.
Signals employed.—The signalman is the responsible person, and must be very vigilant all the time the diver is down; occasionally he will give one pull on the life line, and the diver should return the signal by one pull signifying "all right;" if the signal be not returned, the diver must be hauled up, but if the diver wishes to work without being interrupted by signal, he gives one pull on the line, independently, for "All right; let me alone." If the signalman feels any irregular jerks, such as might be occasioned by the diver falling into a hole, he should signal to know if he is all right, and if he does not receive any reply, he should haul him up immediately. If the diver from any cause is unable to ascend the ladder, and wishes to be pulled up, he gives four sharp pulls on the life line. If while being hauled up the diver gives one pull, it signifies "All right; don't haul me any more." The diver should be hauled up slowly and steadily. If the signalman wishes the diver to come to the surface, he gives four sharp pulls on the line, on which the diver should answer "All right," return to the foot of the ladder, and signal to be hauled up.
One pull on the air-pipe signifies that the diver wants more air. Two pulls on the life line and two pulls on the air-pipe in rapid succession, signify that the diver is foul and cannot release himself, and requires the help of another diver; on receiving such a signal, no attempt should be made to haul the diver to the surface.
The above signals are to be invariably used; but other signals may be arranged as is most convenient for any particular work, as a great variety can be made with the life line and air-pipe. The diver can communicate with the surface by means of a slate.
Further information on this subject, especially with regard to the foregoing diving apparatus, will be found in Messrs. Siebe and Gorman's "Manual for Divers."