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num wire already described, using the three-strand conductors led through water in the tank of the Medical College.
The result was, that the conductors being three inches apart from each other, and prevented from mutual contact by pieces of wood, as shewn in fig. 5, the platinum wire ignited gunpowder in a bottle under water, to a distance one-third the length of that at which explosion would occur were the conductors dry.
This fact enabled me in the explosion of the barque "Equitable," hereinafter described, to dispense with the insulation of the conductors altogether, and to use naked three-strand wires, in the ladder-form, as represented in the plate.
It was manifest 'however that the water did interfere so much as to cut off two-thirds of the electricity in circulation from the standard battery employed. It was also found that approximating the wires towards each other to the distance of one and a half inch, produced a nearly proportionate diminution of the igniting distance. But separating the wires to the distance of three feet did not, on the other hand, materially lengthen the igniting distance. I did not attempt to trace the law by which this effect is regulated-neither time nor means were at my command to do so. But from one and a half inch to three feet constituted the limits within which, in a practical point of view, it was of the least interest to study the phenomenon.
Floating conductors, construction of The preceding experiments made it manifest that to effect subaqueous explosions in fresh water with perfect certainty, naked wires, three inches apart, might be used to the distance or depth of 130 feet. It next became a point of interest to learn how far the distance might be extended by floating or insulating the portion of wires not necessarily immersed in water.
Several plans for floating the wires were tried; for example, earthen pots kept at a distance by slips of bamboo were used, but found very unmanageable, the breakage of one pot frequently throwing the whole line into confusion, and sinking so many of these frail vessels as to prevent any certain results being obtained.
I then tried corks, and with complete success. One of the conductors was led through the axis of each cork, and the cork slided along; as it reached its place a brush dipped in melted pitch was applied round the wire, and the cork shoved on the pitched part. In a few seconds the pitch set, and was protected by the cork. The entire of one conductor, 480 feet in length, was thus coated, and at an expense I may observe of fifteen rupees for all the corks required. *
To the side of this corked wire the second conductor was lashed on by turns of cord. On placing the entire in the tank, I found, to my great satisfaction, that the conductors floated freely, were flexible, light, and manageable in every direction, and that with the battery all along employed, the standard platinum wire was ignited to the same distance as when the conductors were used on land.
Mode of insertion and protection of the platinum wire in the mine.
These experiments left nothing to be desired so far as the battery and conductors were concerned. The next circumstance to be attended to, was the best manner of inserting the platinum wire into the charge of powder, so as to ensure explosion without risking the entrance of water, and with such arrangements as would protect the wires from sudden strains, which might endanger their being torn asunder.
Colonel Pasley, of Chatham, was reported to have led the terminations of the wires through corks, and then to have poured on a cement composed of suet, wax, and pitch. I speak vaguely, not being in full possession of the particulars of Colonel Pasley's method. His conductors were made of wire led through ropes, well insulated by pitch, and surrounded by tarred yarn. It is said that the heavy strain of these rope-conductors frequently tore the wires from the cement, destroyed the platinum loop, and prevented the desired explosion. I do not make this statement in full knowledge of the facts,—it is moreover my most anxious wish not to misrepresent this very distinguished officer ; but my object in preparing for the explosion of the “Equitable” was to guard against the evils attributed to Colonel Pasley's system, by common report and newspaper statements.
* Sola (the subaqueous spongy stems of Æschynomen e. paludosa of Roxburgh) was tried, but was found too brittle and weak.
My apparatus was thus prepared, see fig. 7-fifteen inches of the thick end of a gun-barrel 9, 9, were cut off, and a male screw turned on the barrel near its centre. To this screw was fitted a square plate of iron, half an inch thick by about five inches square i, i, having a hole at each angle to admit of fastening screws being inserted. A teak rod t, t, eighteen inches long, was now prepared so that it would just enter the gun-barrel when nearly red hot-two grooves were cut in the opposite sides of this rod, and the conducting wires let into the grooves and securely fastened in with a strip of wood and pitch cement. The rod and wires were then driven into the hot gun-barrel, and the whole immediately plunged in cold water. The contraction which ensued bound the rod and wires so firmly that no force could possibly affect the platinum loop, nor any leakage occur through the iron tube.
An inch and a half of platinum wire (p) was next soldered to the end of the conductors, and over these was tied a paper cartridge containing mealed Dartford powder-the cartridge was protected by a copper tube G, which screwed on to the end of the gun-barrel, and projected about three inches beyond the platinum loop. This tube was filled with Dartford powder and securely closed by a wooden stopper, cemented into its place by melted pitch.
The ignition of the platinum wire would explode the cartridge, and this the surrounding Dartford powder, which must burst the tube and explode the contents of the mine in which it was placed.
I may here advantageously anticipate the regular course of this narrative by stating, that the mine for the destruction of the Equitable" consisted of a barrel-shaped wooden vessel, about seven feet long by three and a half feet in diameter, capable of containing 2,500lbs. of pow. der. The square iron plate i, i, fig. 7. B, was screwed into the side of this vessel, which was subsequently enclosed in thick sheet lead. Into the iron plate the priming tube, above described, was firmly screwed, a washer of lead being placed in the joint.
Description of self-acting apparatus for igniting the wire at any given
moment. In compliance with the wishes of Captain Fitzgerald, the engineer officer in charge of the operations for destroying the wreck, it was determined to sacrifice the battery employed, by placing it immediately over the mine-it therefore became necessary to contrive some self-acting apparatus by means of which the requisite contact of the conductors with the battery could be made at any desired period.
Bearing in mind that all that is required to prevent the ignition of the platinum wire is to cut, or otherwise interrupt, one of the conductors-or else to bring the wires into metallic contact with each other between the battery and the platinum loop-it will be easy to understand the action of the two pieces of apparatus which I now proceed to describe.
The first of these acts by restoring contact between the ends of a divided conductor, thus completing the electric circuit and igniting the wire. But as some unforeseen accident might interfere, and render it necessary to examine the whole arrangement after the mine was laid, a contrivance was added, which after an interval of four minutes would break the circuit again and render every thing safe during examination.
This apparatus is shewn at fig. 8. It consists of a watch from which the minute hand was removed, and its place supplied by a strip of copper four inches long and a quarter of an inch broad, and fixed by its centre to the arbor of the minute hand. Each end of this index carried by a thread a wire bent thus n, the legs dipping into glass tubes fixed in wood, and containing a portion of mercury. As the copper index revolved, its advancing arm gradually lowered the bent wire a a into the tubes, and thus established contact with the battery, one of the conductors of which c, was interrupted at d and e. The opposite arm, also connected with a bent wire 6 b, would lift this from a similar pair of tubes after a lapse of four minutes, and thus break the contact should no explosion have occurred.
A glance at the figure in the plate will render the plan at once intelligible.
This apparatus could be set so as to go for any period from one to thirteen minutes. The watch employed cost twenty-five rupees.
The second self-acting contrivance was perhaps the simpler of the two, and depended on the fact, that if the conductors come into metallic contact with each other between the battery and the platinum wire, the electricity does not reach the latter, and no ignition occurs,parting the conductors directs the electric fluid upon the platinum wire, and ignition accordingly ensues.