[2] Reinke, Die Welt als That; Berlin, 1899.
[3] In an article on the experimental method recently published in the Dictionnaire de Physiologie, M. Ch. Richet writes as follows:—“We must therefore never cease to carry out comparative experiments. I do not hesitate to say that this comparison is the basis of the experimental method.” It is in fact what was taught by Claude Bernard in maxim and by example. It is no exaggeration to assert that nine-tenths of the errors which take place in research work are imputable to some breach of this method. When an investigator makes a mistake, save in the case of material error, it is almost certainly due to the fact that he has neglected to carry out one of the comparative tests required in the problem before him. The following is an instance which happened since the above pages were written:—Several years ago a chemist announced the existence in the blood serum of a ferment, lipase, capable of saponifying fats—that is to say, of extracting from them the fatty acid. From this he deduced many consequences relative to the mechanism of fermentations. But on the other hand, it has been since shown (April 1902) that this lipase of the serum does not exist. How did the error arise? The author in question had mixed normally obtained serum with oil, and he had noted the acidification of the mixture; he assured himself of the fact by adding carbonate of soda. He saw the alkalinity of the mixture, serum + oil + carbonate of soda, diminish, and he drew the conclusion that the acid came from the saponified oil. He did not make the comparative test, serum + carbonate of soda. If he had done so, he would have ascertained that it also succeeded, and that therefore as the acid did not come from the saponification of the oil, since there was none, its production could not prove the existence of a lipase.
[4] Le Dantec has objected to this conception of phenomena common to different living beings. He insists that all phenomena which take place in a given living being are proper to him, and differ, however slightly, from those of another individual. The objection is more specious than real.
[5] Mayer’s claim to fame has been disputed. A Scotch physicist, P. G. Tait, has investigated the history of the law of the conservation of energy, which is the history of the idea of energy. The conception has taken time to penetrate the human mind, but its experimental proof is of recent date. P. G. Tait finds an almost complete expression of the law of the conservation of energy in Newton’s third law of motion—namely, “the law of the equality of action and reaction,” or rather, in the second explanation which Newton gave of that law. In fact, it was from this law that Helmholtz deduced it in 1847. He showed that the law of the equality of action and reaction, considered as a law of nature, involved the impossibility of perpetual motion, and the impossibility of perpetual motion is, in another form, the conservation of energy.
At a meeting of the Academy of Science, at Berlin, 28th March 1878, Du Bois-Reymond violently attacked Tait’s contention. The honour of having been the first to conceive of the idea of energy and conservation was awarded to Leibniz. Newton had no right to it, for he appealed to divine intervention to set the planetary system on its path when disturbed by accumulated perturbations. On the other hand, Colding claims to have drawn his knowledge of the law of conservation from d’Alembert’s principle. Whatever may be the theoretical foundations of this law, we are here dealing with its experimental proof. According to Tait, the proof can no more be attributed to R. Mayer than to Seguin. The real modern authors of the principle of the conservation of energy, who gave an experimental proof of it, are Colding, of Copenhagen, and Joule, of Manchester.
[6] It must be added that the absolute rigour of this law has been called in question in recent researches. It would only have an approximate value.
[7] The dyne is the force which applied to the unit of mass produces a unit of acceleration.
[8] These words spoil the statement, for time has nothing to do with it.
[9] We therefore notice that the measures of force and work bring in mass, space, and time. The typical force, weight, is given by w = mg. On the other hand, we have by the laws of falling bodies v = gt; s = 1∕2gt2; whence g = 2s∕t2; w = m(2s∕ t2); or, if F be the force, M the mass, L the space described, and T the time, we have F = MLT-2, which expresses what are called the dimensions of the force—that is to say, the magnitudes with their degree, which enter into its expression. We may thus easily obtain the dimensions of work:—
Work = f × s = mv2∕2 = ML2T-2.