Now there is one object which the chemists often have in view, when they put different kinds of substances together, in a dissolved or liquid state, in the chambers and vessels of their laboratories; that is, to get something out of those substances, which was before hidden away in them, in order that they may turn that something to practical use. Thus the chemist mixes together saltpetre, sulphur, and charcoal in the right proportions to make gunpowder. Then having rammed a charge of the gunpowder down into the tube of a gun, with a bullet on the top of a charge, he applies a spark to the gunpowder, and makes it change into smoke and vapor. Something which was hidden away in the gunpowder ceases to be concealed when it is changed into smoke and vapor, and becomes active enough to be able to drive the bullet out of the muzzle of the gun with a force that carries it through the air for a mile, and perhaps then buries it deep in the ground, or in a plank of wood. This is an instance of the way in which chemists produce motion, by changing the state and condition of material substance. I had occasion the other day to watch a still more interesting example of this strange result of the chemist’s skill. In a chemist’s laboratory, prepared for a particular service, I saw several small chambers of metal, half copper and half zinc, into which were poured blue vitriol and water, and an acid, a partition wall of pipe-clay standing between. The dilute acid and the zinc were slowly turning into white vitriol, which remained dissolved away in the water; but out of this new-made white vitriol there flowed a power, which was conveyed along a wire, and which made a needle, hung up on a pivot before me, twitch from side to side, almost as if it had been a living thing. I was told that this power set free in the solution, in consequence of the changes brought about there, would run along the wire to the distance of a hundred, or even of a thousand miles, and would there make another needle work and twitch in the same way. In short, I was looking at the electric telegraph at work, and learning that the agent which made the signal afar was simply a power that had been hidden away in the different substances the chemist put together in the metal chambers, and that was set free and enabled to operate in the production of independent motion, so soon as those substances acted upon one another, and altered the form and state in which each was existing.