The young lieutenant smiled rather broadly as he explained, in a glib and slightly sing-song tone, which savoured of the Woolwich Military Academy, that, "gun-cotton is the name given to the explosive substance produced by the action of nitric acid mixed with sulphuric acid, on cotton fibre." He was going to add, "It contains carbon, hydrogen, nitrogen, and oxygen, corresponding to--" when my mother stopped him.

"Dear me, Mr Firebrand, is a _popular_ explanation impossible?"

"Not impossible, madam, but rather difficult. Let me see. Gun-cotton is a chemical compound of the elements which I have just named--a _chemical compound_, you will observe, not a mechanical _mixture_, like gunpowder. Hence it explodes more rapidly than the latter, and its power is from three to six times greater."

My mother looked perplexed. "What is the difference," she asked, "between a chemical compound and a mechanical mixture?"

Firebrand now in his turn looked perplexed. "Why, madam," he exclaimed, in modulated desperation, "the ultimate molecules of a mixture are only placed _beside_ each other, so that an atom of gunpowder may be saltpetre, charcoal, or sulphur, dependent on its fellow-atoms for power to act; whereas a chemical compound is such a perfect union of substances, that each ultimate molecule is complete in its definite proportions of the four elements, and therefore an _independent_ little atom."

"Now, the next experiment," continued Firebrand, glad to have an opportunity of changing the subject, "is meant to ill.u.s.trate our method of countermining. You must know that our enemies may sometimes sink torpedoes at the entrance of their harbours, to prevent our ships of war entering. Such torpedoes consist usually of casks or cases of explosives, which are fired either by electric wires, like the telegraph, when ships are seen to be pa.s.sing over them, or by _contact_.

That is to say, an enemy's ship entering a harbour runs against something which sets something else in motion, which explodes the torpedo and blows it and the ship into what natives of the Green Isle call smithereens. This is very satisfactory when it happens to an enemy, but not when it happens to one's-self, therefore when _we_ have to enter an enemy's harbour we _countermine_. This operation is now about to be ill.u.s.trated. The last experiments exhibited the power of offensive torpedoes. There are several different kinds, such as Mr Whitehead's fish-torpedo, the Harvey torpedo, and others."

"Dear me," said my mother, with a perplexed air, "I should have thought, Mr Firebrand, that all torpedoes were offensive."

"By no means; those which are placed at the entrance of harbours and navigable rivers are defensive. To protect ourselves from the offensive weapon, we use crinolines."

My mother looked quickly up at her polite young mentor. "You play with the ignorance of an old woman, sir," she said, with a half-jocular air.

"Indeed I do not, madam, I a.s.sure you," returned Firebrand, with much earnestness. "Every iron-clad is provided with a crinoline, which is a powerful iron network, hung all round the ship at some distance from her, like--pardon me--a lady's crinoline, and is intended to intercept any torpedo that may be discharged against her."

Attention was called, at this point, to the counter-mining experiments.

It may be said, in regard to these, that they can be conducted in various ways, but always with the same end in view, namely, to destroy an enemy's mines by exploding others in their midst.

For the sake of ill.u.s.tration, it was supposed that the surrounding sea-bottom was studded with invisible torpedoes, and that the _Nettle_ was a warship, determined to advance into the enemy's harbour. To effect this with safety, and in order to clear away the supposed sunken torpedoes, a counter-torpedo was floated between two empty casks, and sent off floating in the desired direction by means of the tide. This countermine consisted of an iron cylinder, containing 300 pounds of powder, and was electrically connected with the _Nettle_. A small charge of gun-cotton was fixed to the suspender that held the torpedo to its casks. When at a safe distance from the ship, this charge was fired. It cut the suspender and let the torpedo sink to the bottom.

There it was exploded with terrific violence, as was quickly shown by the mighty fountain of mud, water, and smoke that instantly shot up into the air. It has been proved by experiment that 500 pounds of gun-cotton exploded below water, will destroy all the torpedoes that lie within a radius of 120 yards. It is obvious, therefore, that a warship could advance into the s.p.a.ce thus cleared and then send a second countermine ahead of her in the same way. If neither tide, current, nor wind will serve to drift the casks, the operation might be accomplished by a small boat, which could back out of danger after laying each torpedo, and thus, step by step, or shot by shot, the advance could be made in safety through the enemy's defences.

After this, twelve small charges of gun-cotton were sunk in various directions, each representing a countermine of 500 pounds. These were discharged simultaneously, to demonstrate the possibility of extending the operations over a wide area. These miniature charges were sent down in small nets, and were quite unprotected from the water, so that the gun-cotton was wet when fired.

This fact caught the attention of my mother at once.

"How can it go off when _wet_?" she exclaimed, turning her bright little eyes in astonishment on her young companion.

"Ha, that is one of the strange peculiarities of gun-cotton," replied Firebrand, with an amused look; "you don't require to keep it dry like powder. It is only necessary that there should be one small lump of dry gun-cotton inside the wet stuff, with a detonator in its heart. A detonator, you must know--"

"Oh, I know what a detonator is," said my mother, quickly.

"Well then," continued Firebrand, "the exploding of the detonator and the dry disc causes the wet gun-cotton also to go off, as you have seen.

Now they are going to exhibit one of the modes of defending harbours.

They have sunk four mines, of 300 pounds of gunpowder each, not far from where you see yon black specks floating on the water. The black specks are buoys, called _circuit-closers_, because they contain a delicate contrivance--a compound of mechanism and galvanism--which, when the buoys are b.u.mped, _close_ the electric circuit and cause the mine to explode. Thus when a ship-of-war sails against one of these circuit-closers, she is immediately blown up."

"Is not that rather a sneaking way of killing one's enemies?" asked my mother.

Young Firebrand laughed, and admitted that it was, but pleaded that everything was fair in love and war.

In actual warfare the circuit-closers are placed just over the mines which they are designed to explode, but for safety on this occasion they were placed at a safe distance from their respective mines. A steam-launch was used to b.u.mp them, and a prodigious upheaval of water on each explosion showed clearly enough what would have been the fate of an iron-clad if she had been over the mine.

"Oh, shade of Nelson!" I could not help exclaiming, "how shocked you must be if you are permitted to witness such methods of conducting war."

"Ah, yes!" sighed Firebrand; "the bubble reputation, you see, is being transferred from the cannon's mouth to the torpedo."

I made no reply, for my mind reverted to my laboratory in Devonshire, where lay the working-model of the terrible weapon I had spent so much time in perfecting. It seemed strange to me now, that, in the eager pursuit of a scientific object, I had scarcely ever, if at all, reflected on the dire results that the use of my torpedo involved, and I felt as if I were really guilty of the intent to murder. Just before leaving home I had charged my model, which was quite a large one, capable of holding about 50 pounds of dynamite, in the hope that I might prevail on the First Lord of the Admiralty and some of his colleagues to come down and see it actually fired. I now resolved to throw the dynamite into the sea, break up my model, and have done with explosives for ever.

While my mind was running on this, I was startled by an explosion close alongside. On turning towards the side of the ship, I found that it was caused by the rending of a huge iron chain, the links of which were more than one and a quarter inch in thickness. This powerful cable, which could have held an iron-clad, was snapped in twain like a piece of thread by the explosion _against_ it of only two and a half pounds of gun-cotton.

"Very well done," I said to Firebrand, "but I think that a much smaller quant.i.ty of dynamite would have done it as effectively."

"Now, Mrs Childers," said the young lieutenant, "the last experiment is about to be made, and I think it will interest you even more than the others. See, they are about to send off the electrical steam-pinnace."

As he spoke, a boat was being prepared alongside the ship.

"Why!" exclaimed my mother, almost speechless with surprise, "they have forgotten to send its crew in it."

"No, madam," said Firebrand, with one of his blandest smiles, "they have not forgotten her crew, but there are services so dangerous, that although the courage of the British sailor will of course enable him to face _anything_, it has been thought advisable not to put it to too severe a test, hence this automatic boat has been invented. It is steered, and all its other operations are performed, by means of electricity, applied not on board the boat but on board of the _Nettle_."

This was indeed the case. The electric pinnace went off as he spoke, her steam-engines, steering-gear, and all the other apparatus being regulated by electric wires, which were "paid out" from the ship as the boat proceeded on her mission of supposed extreme danger. Right under the withering fire of the imaginary enemy's batteries she went, and having scorned the rain of small shot that swept over her like hail, and escaped the plunging heavy shot that fell on every side, she dropped a mine over her stern, exploded it by means of a slow fuse, turned round and steamed back in triumph, amid the cheers of the spectators.

This last was really a marvellous sight, and the little boat seemed indeed to deserve the encomiums of Firebrand, who said, that, "If cool, calm pluck, in the face of appalling danger, merited anything, that heroic little steam-pinnace ought to receive the Victoria Cross."

I was still meditating on this subject, and listening to the animated comments going on around me, when I myself received a shock, compared to which all the explosions I had that day witnessed were as nothing.

It suddenly recurred to my memory that I had left a compound in my laboratory at home in a state of chemical preparation, which required watching to prevent its catching fire at a certain part of the process.

I had been called away from that compound suddenly by Nicholas, just before we left for London, and I had been so taken up with what he had to tell me, that I had totally forgotten it. The mere burning of this compound would, in itself, have been nothing, for my laboratory was an old out-house, quite unconnected with the dwelling; but in the laboratory also lay my torpedo! The worst of it was that I had inserted a detonator and affixed a fuse, feeling quite secure in doing so, because I invariably locked the door and carried the key in my pocket.

My face must have turned very pale, for Nicholas, who came up at the moment, looked at me with anxious surprise, and asked if I were ill.

"No," said I, hurriedly; "no, not ill--but--yes--it is a slow process at best, and not always certain--sometimes takes a day or two to culminate.

The fusion may not have been quite completed, or it may have failed altogether. Too late, I fear, too late, but I cannot rest till I know.

Tell my mother I'm off home--only business--don't alarm her."

Regardless of the amazed looks of those who stood near me, I broke from the grasp of Nicholas, leaped into one of the boats alongside, seized the oars, and rowed ash.o.r.e in mad haste.

Fortune favoured me. The train had not left, though it was just in motion. I had no time to take a ticket, but leaping upon the moving footboard, I wrenched open a carriage-door and sprang in.

It was an express. We went at full sixty miles an hour, yet I felt as if we moved like a snail. No words can adequately explain the state of my mind and body--the almost uncontrollable desire I felt to spring out of the train and run on ahead. But I was forced to sit still and think.

I thought of the nearness of the laboratory to our kitchen windows, of the tremendous energy of the explosive with which the model-torpedo was charged, of the ma.s.s of combustibles of all kinds by which it was surrounded, of the thousand and one possibilities of the case, and of my own inexcusable madness in not being more careful.

At last the train pulled up at the town from which our residence is about two miles distant. It was now evening; but it was summer, and the days were long. Hiring a horse at the nearest hotel, I set off at a break-neck gallop.

The avenue-gate was open. I dashed in. The laboratory was not visible from that point, being at the back of the house. At the front door I pulled up, sprang to the ground, let the horse go, and ran forward.

I was met by Lancey coming round the corner. I saw at once that all was over! His face and hands had been scorched, and his hair singed! I gasped for breath.

"No one killed?" I asked.

"No, sir, n.o.body killed, but most of us 'orribly scared, sir."

"n.o.body hurt, Lancey?" I asked again, leaning against the side of the house, and wiping my forehead.