380 CORRELATION OF FORCES heat radiated from the sun would be sufficient to raise from freezing to boiling 700,000,000,- 000 cubic miles of water each hour. Solar heat, by the evaporation of water from the terrestrial surface, raises it to the potential state of atmospheric vapor, which precipitated as rain maintains the conditions of organic life upon the land, and gives rise to watercourses, which sweep down the soil to the lower levels, and thus become sources of geological change. As the water descends it is made to turn wheels, and becomes available as water power. Solar heat at the same time expands the air and gives rise to atmospheric currents, which by turning wheels in the air or propelling ships is made available as wind power. The total amount of solar heat falling annually upon a square foot of land in lat. 50 is equal, according to Thomson, to 530,000,000 foot pounds ; and of this he estimates that about 01 is spent upon the vegetable kingdom in impelling changes of growth and secretion. Under the influence of light the green parts of plants decompose carbonic acid, water, and ammonia, and the plant then works up the elements into its peculiar organic compounds, which thus become depositories of solar force. By the slow process of natural decay these compounds are disintegrated, and their ele- ments fall from the organic to the inorganic stage, and in the successive stages of decom- position give out their stored forces as heat, which is taken up by surrounding bodies or diffused into space. By the quick combustion of organic compounds, the stored force is given back with such intensity that it may be made available for mechanical effects. The particles of a pound of coal when burnt fall to the mineral state, and give out power enough to raise from 5,000,000 to 10,000,000 Ibs. a foot high. The steam engine is thus driven by the solar energy accumulated in fuel. The vege- table kingdom is thus designed to accumulate force, the animal kingdom to expend it. Their operations are antagonized, as was first shown in detail by Dumas and Boussingault in an ad- mirable little work entitled " The Balance of Organic Nature." They there showed that while the office of vegetables is constructive, that of animals is destructive. Plants decompose carbonic acid, water, and mineral salts ; animals produce them. Plants form organized com- pounds ; animals destroy them. Plants absorb force ; animals give out or expend force. The animal body is hence a dynamic engine, with no capacity of creating force, and which can only make use in various ways of that which is stored up in the food consumed. The relation between food and work has lately occupied much of the attention of physiologists, who have aimed to determine the connection be- tween animal excretions of different kinds, and the elementary matters ingested and the prod- ucts excreted. The first use of food is for growth or animal construction; but when the bones, muscles, brain, and other organs FOOD. In combustion raises Ibs. of water 1 deg. F. Which is equal to lifting lb. 1 foot high. 10 grata s of dry flesh 18-12 12-85 8-61 10-06 18-68 20-91 10,128 9,920 6,647 7,766 14,421 16,142 " albumen " lump sugar " arrowroot " butter " beef fat . are developed and the adult state is reached, the first use for food disappears, and a bal- ance is struck between the income and the expenditure of the system. Foods being re- garded generally as sources of power, without reference to the way they are used, they have very different values in this respect. Dr. Ed- ward Smith, in his excellent work " On Foods," says that an ounce of fresh lean meat, if en- tirely burnt in the body, would produce heat sufficient to raise about 70 Ibs. of water 1 F., or a gallon of water about 7 F. In like man- ner one ounce of fresh butter would produce about ten times that amount of heat ; but it must be added that, as the combustion which is effected within the body is not always com- plete, the actual effect is less than that now indicated. Dr. Smith states the results of Prof. Frankland's researches into the dynamic effects of different elementary principles as follows : The amount of power which the average man is capable of exerting in a given time, and the relative amounts that are expended in different ways, have been proximately determined ; but the difficulty of investigation will probably long be a cause of disagreement in results. The measured products of physiological change are indices of the force developed in such change. Dr. Edward Smith has estimated the daily ex- cretion of carbon in the form of carbonic acid from the lungs, in the case of four persons, as follows : PERSONS. Body weight, Ibs. Carbon, oz. Mr. Moul 178 6-785 Dr E Smith 196 7-850 Prof. Frankland 186 5-600 Dr Murie 138 6-540 These data, converted into vertical miles through which the body weight is lifted by the carbon consumed, give the following ele- vations : Mr. Moul 5-17 miles. Dr. E. Smith 5-32 " Prof. Frankland 5-47 " Dr. Murie 6 53 It is obvious that the carbonic acid from the skin and the kidneys, if taken into account, would here increase the mechanical effect. Much the largest portion of food consumed in the system goes for the production of animal heat. In the diet of infants, in which growth is to be provided for, the ratio of tissue-form- ing to heat-producing elements is about one to three. When growth ceases this relation is
