Thus, if we were asked, What is sulphur? or what is selenium? we should at least be able to reply, A form of matter; and then proceed to describe its properties, i. e., how it affected our bodies and other bodies.
Again, to the question, What is heat? we can reply, A form of energy; and proceed to describe the peculiarities which distinguish it from other forms of energy.
But to the question. What is electricity? we have no answer pat like this. We can not assert that it is a form of matter, neither can we deny it; on the other hand, we certainly can not assert that it is a form of energy, and I should be disposed to deny it. It may be that electricity is an entity per se, just as matter is an entity per se.
Nevertheless, I can tell you what I mean by electricity by appealing to its known behavior.
Here is a battery, that is, an electricity pump; it will drive electricity along. Prof. Ayrtou is going, I am afraid, to tell you, on the 20th of January next, that it produces electricity; but if he does, I hope you will remember that that is exactly what neither it nor anything else can do. It is as impossible to generate electricity in the sense I am trying to give the word, as it is to produce matter. Of course I need hardly say that Prof. Ayrton knows this perfectly well; it is merely a question of words, i. e., of what you understand by the word electricity.
I want you, then, to regard this battery and all electrical machines and batteries as kinds of electricity pumps, which drive the electricity along through the wire very much as a water-pump can drive water along pipes. While this is going on the wire manifests a whole series of properties, which are called the properties of the current.
[Here were shown an ignited platinum wire, the electric arc between two carbons, an electric machine spark, an induction coil spark, and a vacuum tube glow. Also a large nail was magnetized by being wrapped in the current, and two helices were suspended and seen to direct and attract each other.]
To make a magnet, then, we only need a current of electricity flowing round and round in a whirl. A vortex or whirlpool of electricity is in fact a magnet; and vice versa. And these whirls have the power of directing and attracting other previously existing whirls according to certain laws, called the laws of magnetism. And, moreover, they have the power of exciting fresh whirls in neighboring conductors, and of repelling them according to the laws of diamagnetism. The theory of the actions is known, though the nature of the whirls, as of the simple stream of electricity, is at present unknown.
[Here was shown a large electro-magnet and an induction-coil vacuum discharge spinning round and round when placed in its field.]
So much for what happens when electricity is made to travel along conductors, i. e., when it travels along like a stream of water in a pipe, or spins round and round like a whirlpool.