Fig. 11.
Once more: suppose we have a series of active machines. (Fig. 11.) An arc lamp, radiating light-waves, gets its energy from the wire which is heated, which in turn gets its energy from the electric current; that from a dynamo, the dynamo from a steam-engine; that from a furnace and the chemical actions going on in it. Let us call the chemical actions a, the furnace b, the engine c, the dynamo d, the electric lamp e, the ether waves f. (Fig. 12.)
The product of the chemical action of the coal is molecular motion, called heat in the furnace. The product of the heat is mechanical motion in the engine. The product of the mechanical motion is electricity in the dynamo. The product of the electric current in the lamp is light-waves in the ether. No one hesitates for an instant to speak of the heat as being molecular motion, nor of the
motions of the engine as being mechanical; but when we come to the product of the dynamo, which we call electricity, behold, nearly every one says, not that he does not know what it is, but that no one knows! Does any one venture to say he does not know what heat is, because he cannot describe in detail just what goes on in a heated body, as it might be described by one who saw with a microscope the movements of the molecules? Let us go back for a moment to the proposition stated early in this book, namely, that if any body of any magnitude moves, it is because some other body in motion and in contact with it has imparted its motion by mechanical pressure. Therefore, the ether waves at f (Fig. 11) imply continuous motions of some sort from a to f. That they are all motions of ordinary matter from a to e is obvious, because continuous matter is essential for the maintenance
of the actions. At e the motions are handed over to the ether, and they are radiated away as light-waves.
Fig. 12.
A puzzling electrical phenomenon has been what has been called its duality-states, which are spoken of as positive and negative. Thus, we speak of the positive plate of a battery and the negative pole of a dynamo; and another troublesome condition to idealize has been, how it could be that, in an electric circuit, there could be as much energy at