Fig. 10.—Dynamo and Motor.
Let us suppose ourselves to be in a building in which a steam-engine is at work. There is fuel, the furnace, the boiler, the pipes, the engine with its fly-wheel turning. The fuel burns in the furnace, the water is superheated in the boiler, the steam is directed by the pipes, the piston is moved by the steam pressure, and the fly-wheel rotates
because of proper mechanism between it and the piston. No one who has given attention to the successive steps in the process is so puzzled as to feel the need of inventing a particular force, or a new kind of matter, or any agency, at any stage of the process, different from the simple mechanical ones represented by a push or a pull. Even if he cannot see clearly how heat can produce a push, he does not venture to assume a genii to do the work, but for the time is content with saying that if he starts with motion in the furnace and stops with the motion of the fly-wheel, any assumption of any other factor than some form of motion between the two would be gratuitous. He can truthfully say that he understands the nature of that which goes on between the furnace and the wheel; that it is some sort of motion, the particular kind of which he might make out at his leisure.
Suppose once more that, across the road from an engine-house, there was another building, where all sorts of machines—lathes, planers, drills, etc.—were running, but that the source of the power for all this was out of sight, and that one could see no connection between this and the engine on the other side of the street. Would one need to suppose there was anything mysterious between the two—a force, a fluid, an immaterial something? This question is put on the supposition that one should
not be aware of the shaft that might be between the two buildings, and that it was not obvious on simple inspection how the machines got their motions from the engine. No one would be puzzled because he did not know just what the intervening mechanism might be. If the boiler were in the one building, and the engine in the other with the machines, he could see nothing moving between them, even if the steam-pipes were of glass. If matter of any kind were moving, he could not see it there. He would say there must be something moving, or pressure could not be transferred from one place to the other.
Substitute for the furnace and boiler a galvanic battery or a dynamo; for the machines of the shop, one or more motors with suitable wire connections. When the dynamo goes the motors go; when the dynamo stops the motors stop; nothing can be seen to be turning or moving in any way between them. Is there any necessity for assuming a mysterious agency, or a force of a nature different from the visible ones at the two ends of the line? Is it not certain that the question is, How does the motion get from one to the other, whether there be a wire or not? If there be a wire, it is plain that there is motion in it, for it is heated its whole length, and heat is known to be a mode of motion, and every molecule which is thus heated must have had some
antecedent motions. Whether it be defined or not, and whether it be called by one name or another, are quite immaterial, if one is concerned only with the nature of the action, whether it be matter or ether, or motion or abracadabra.