communicated his ideas to friends, and sought to convince them. The mathematicians among them were so affected by the faulty form in which Mayer put his theory, that they would not listen and paid him no attention, even after he had corrected the error. The professors proved no more amenable. One of them remarked, sarcastically, that if that were so, a bottle of water violently shaken ought to become warmer. Mayer, undeterred by the sarcasm, tried the experiment, the result of which is now so familiar to us as to seem almost axiomatic.
We see clearly that in doing mechanical work the losses of work, due to friction, result in heat. In a word, friction is a means of converting work into heat, just as a steam engine is a means of converting heat into work. Incomplete machines are those that transmute part of the work into heat, and the smaller this part is, the more perfect we call the machine.
Heat is, however, not the only thing into which work may be converted. It may reappear in the form of electricity, or of light, or of chemical change. All these things, out of which work may arise or into which it may be changed, we now call energy. While the law of the conservation of work has only a limited and ideal application, that of the conservation of energy is a natural law of universal application, without any limitation or exception. If we call those amounts of energy equal which arise from one another, we can, as the result of all experience, express the conservation law in the following terms:
Within a closed system, through whose walls no energy can pass in or go out, the total amount of energy remains the same, regardless of what happens inside the system.
In what light are we to consider this energy? Is it an actuality or a mere figment of thought? The reply can scarcely be doubtful. That which can not be created by any power in the universe, which maintains itself unaltered in amount in spite of all the unnumbered and protean changes to which it is subjected through all the ages, must be the most real thing we can conceive of. All efforts of the adherents of the older view to discredit the reality of energy have been fruitless, so that it is now thought of not merely as a formal thing, but as an essential entity, as a commodity which can be measured, stored, bought and sold. When you have the storage battery of your electric car charged up, and pay for it, what are you getting for your money? The battery is not heavier by the smallest fraction of an ounce. You have not purchased a figment of the mind, nor any mere abstraction, but an absolutely real thing, so many units of energy. You may think of it perhaps as electricity, but this is erroneous, since the charged battery contains its energy in chemical, not in electrical form.
Energy is more than a reality. It is the reality. No phenomenon, no effect, is anything but a (more or less transitory) manifestation of energy and, as such, is subject to the energy law.
