[C]onsciousness teaches every individual that they are, to some extent, subject to the direction of his will. It appears, therefore, that animated creatures have the power of immediately applying, to certain moving particles of matter within their bodies, forces by which the motions of these particles are directed to produce desired mechanical effects.2
The question, “Can animated creatures set matter in motion in virtue of an inherent power of producing mechanical effect ?” must be answered in the negative, according to the well-established theory of animal heat and motion, which ascribes them to the chemical action (principally oxidation, or a combustion at low temperatures) experienced by the food. A principal object of the present communication is to point out the relation of this theory to the dynamical theory of heat. It is remarked, in the first place, that both animal heat and weights raised or resistance overcome, are mechanical effects of the chemical forces which act during the combination of food with oxygen. The former is a dynamical mechanical effect, being thermal motions excited ; the latter is a mechanical effect of the statical kind. The whole mechanical value of these effects, which are produced by means of the animal mechanism in any time, must be equal to the mechanical value of the work done by the chemical forces. Hence, when an animal is going up-hill or working against resisting force, there is less heat generated than the amount due to the oxidation of the food, by the thermal equivalent of the mechanical effect produced. From an estimate made by Mr. Joule, it appears that from ~ to ~ of the mechanical equivalent of the complete oxidation of all the food consumed by a horse may be produced, from day to day, as weights raised. The oxidation of the whole food consumed being, in reality, far from complete, it follows that a less proportion than 4, perhaps even less than ~, of the heat due to the whole chemical action that actually goes on in the body of the animal, is given out as heat. An estimate, according to the same principle, upon veryimp effect data, however, is made by the author, regarding the relation between the thermal and the non-thermal mechanical effects produced by a man at work; by which it appears that probably as much as ~ of the whole work of the chemical forces arising from the oxidation of his food during the twenty-four hours, may be directed to raising his own weight, by a man walking up-hill for eight hours a day ; and perhaps even as much as ¼ of the work of the chemical forces may be directed to the overcoming of external resistances by a man exerting himself for six hours a day in such operations as pumping. In the former case there would not be more than 4, and in the latter not more than ¼ of the thermal equivalent of the chemical action emitted as animal heat, on the whole, during the twenty-four hours, and the quantities of heat emitted during the times of working would bear much smaller proportions respectively than these, to the thermal equivalents of the chemical forces actually operating during those times.
A curious inference is pointed out, that an animal would be sensibly less warm in going up-hill than in going down-hill, were the breathing not greater in the former case than in the latter.
The application of Carnot’s principle, and of Joule’s discoveries regarding the heat of electrolysis and the calorific effects of magneto-electricity, is pointed out ; according to which it appears nearly certain that, when an animal works against resisting force, there is not a conversion of heat into external mechanical effect, but the full thermal equivalent of the chemical forces is never produced; in other words, that the animal body does not act as a thermo-dynamic engine ; and very probable that the chemical forces produce the external mechanical effects through electrical means.
Certainty regarding the means in the animal body by which external mechanical effects are produced from chemical forces acting internally, cannot be arrived at without more experiment and observation than has yet been applied; but the relation of mechanical equivalence, between the work done by the chemical forces, and the final mechanical effects produced, whether solely heat, or partly heat and partly resistance overcome, may be asserted with confidence. Whatever be the nature of these means, consciousness teaches every individual that they are, to some extent, subject to the direction of his will. It appears, therefore, that animated creatures have the power of immediately applying, to certain moving particles 6f matter within their bodies, forces by which the motions of these particles are directed to produce desired mechanical effects.
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