Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

    484/502 page 464
    Energ-y is thus of different qualities, mechanical energy being the best, and universal heat the worst: in fact, this latter description of energy may be compared to the waste heap of the universe, in which the effete forms of energy are suffered to accumulate, and this waste heap is always continuing to in- crease. But before attempting to discuss the probable effect of this process of deterioration upon the present system of things, let us look around us and endeavour to estimate the various sources of energy that have been placed at our dis- posal. 454. Sources of Energy.—To begin with our own frames. We all of us possess a certain amount of energy in our systems, a certain capacity for doing work. By an effort of his muscles the blacksmith imparts a formidable velocity to the massive hammer which he wields. Now what is consumed in order to produce this ? We reply, the tissues of his body are con- sumed. If he continues working for a long time, he will wear out these tissues and nature will call for food and rest—for the former in order to procure the materials out of which new and energetic tissues may be constructed ; for the latter, in order to furnish time and leisure for repairing the waste. Ultimately, therefore, the energy of the man is derived from the food which he eats ; and it he works much, that is to say, spends a great deal of energy, he will require to eat more than if he hardly works at all. Hence it is well understood that the diet of a man sentenced to imprison- ment with hard labour must be more generous than that ot one who is merely imprisoned, and that the allowance of food to a soldier in time of war must be greater than in time of peace. In fact, food is to the animal what fuel is to the engine, only an animal is a much more economical producer ot work than an engine. Rumford justly observed that we shall get more work out of a ton of hay if we give it as food to a horse, than if we burn it as fuel in an engine. It is in truth the combustion of our food that turnishes our fr.imes with eni'i gy, and there is no food c.ipable ot nourishing our bodies which, if well ilried, is not .ilso capable ot being burned in the fne. Having thus tr.ieed the energy ot our frames to the food which we eat, we next ;isk, whence does food derive its energy? If we ;ire vegetarians, we need not
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