When a man works he uses up fuel. If a blacksmith heats a piece of iron by hammering, the heat given to the iron and the heat produced in his body are together equal to the heat of the fuel consumed in his blood. The work a man does, as well as the heat of his body, comes from the burning of the fuel in his blood.
What is true of a man is true of an engine. The work the engine does, as well as the heat it produces, comes from the heat of the fuel in the furnace. Mayer found that one hundred pounds of coal in a good working engine produces the same amount of heat as ninety-five pounds in an engine that is not working. In the working engine the heat of the five pounds of coal is used up in the work of running the engine, and therefore does not heat the engine. Heat that is used in running the engine is no longer heat, but work. So Mayer said the heat is not destroyed, but only changed into work. He said, further, that the work of running the engine may be changed again into heat.
Mayer's theory was opposed by many scientific men of Europe. One great scientist said to him that if his theory were correct water could be warmed by shaking. He remembered what the helmsman had remarked to him on the voyage to Java, that water beaten about by a storm is warmer than quiet sea-water; but he said nothing. He went to his laboratory, tried the experiment, and some weeks later returned, exclaiming: "It is so! It is so!" He had warmed water simply by shaking it.
These results mean that work or energy cannot be destroyed. Though it changes form in many ways, it is never destroyed. Neither can man create energy; he can only direct its changes as the engineer, by the motion of his finger in opening a valve, sets the locomotive in motion. He does not move the locomotive. He directs the energy already in the steam.
Since the time of Galileo, men had caught now and then a glimpse of this great law. Galileo had stated his law of machines; that, when a machine does work, a man or a horse or some other power does an equal amount of work upon the machine. Count Rumford had performed his experiment with the cannon, showing that heat is produced by the work of a horse. Davy had proved that, in the voltaic battery, something must be used up to produce the current—the mere contact of the metals is not sufficient. Faraday had said that in no case is there a production of electrical power without something being used up to supply it. Mayer stated clearly this law of energy when he said that energy cannot be created or destroyed, but only changed from one form to another.
And yet inventors have not learned the meaning of this law. They continue trying to invent perpetual-motion machines—machines that will produce work from nothing. This is what a perpetual-motion machine would be if such a machine were possible. For a machine without friction is impossible, and friction means wasted work—work changed into heat. A machine to keep itself running and supply the work wasted in friction must produce work from nothing. The great law of nature is that you cannot get something for nothing. Whether you get work, heat, electricity, or light, something must be used up to produce it. For whatever you get out of a machine you must give an equivalent. This law cannot be evaded, and from it there is no appeal.
Chapter V
GREAT INVENTIONS OF THE NINETEENTH CENTURY
The discoveries of Faraday prepared the way for the great inventions of the nineteenth century. By the middle of the century men knew how to control the wonderful power of electricity. They did not know what electricity is, nor do we know to-day, though we have made some progress in that direction; but to control it and make it furnish light, heat, and power was more important.