“I don’t know,” replied Dennis; “no one knows beyond that it is some untarnishable alloy, probably from the fact that no one can examine it. See, I throw this hammer at it and you will see it de-atomise,” saying which, with a fine disregard of tools, he lifted up a heavy steel hammer and flung it at the vessel, but when it came within about a foot of the side it suddenly vanished and there appeared a little puff of faint, thin vapour—the gaseous atoms of the missile—which became mixed with and lost in the air of the shed. “There’s an enormous force there,” observed Ross, amazed. “What generates it? Batteries?” “No one knows,” answered Dennis, “that is one of the mysteries. If it came from the engines or dynamos on the vessel, they would have been run out or worn out ages ago; we should also hear motion of some kind, but you will notice everything is silent as the grave. Listen!” and they all remained mute and motionless for a few minutes, but not a sound disturbed the vault-like quietude. “Batteries would be equally out of the question,” remarked Gilbert; “apart from the quantity needed to give a constant current of that strength, they would require recharging and replenishing, and perpetual motion has not yet been discovered.” “That is so,” agreed Ross. “I think we must seek some other cause, some means by which the force is spontaneously extracted from the air or earth around. You know our airships have no engines to drive the motors; we gather the necessary power for this direct from the air by the aid of certain metals which, when alloyed in given proportions, attract electricity to any desired volume and under perfect control, and I think some such force is here. Have you tried any of the active metals?” “Yes, all; everything!” replied Dennis. “She is a strange anomaly; she has engines and motors which are necessary for her flight in some way, and yet there is a continuous current, as you see, which apparently comes from nowhere. And one would think that if such a force is self-generating, engines and motors would not be necessary. The whole thing is a mystery; especially when you consider that one might almost imagine her to be alive, or that some demon is on board who manipulates the forces, for if any electric energy or metal comes in her vicinity, she seems to get her blessed temper up and literally fights. At the mere approach she crackles all over and throws out sparks of fire and lightning that have more than once blasted the shed to the ground, and everything has had to be strongly insulated, or there would be an electric storm;” and Dennis drew their attention to the building, saying, “You will notice all the tools are insulated and the whole interior of the shed lined with sheets of thick glass cemented together, the masonry and shutters being on the outside.”