"But there is this marked contrast between the two kingdoms of organic nature in their material and dynamic relations to the inorganic world: that while the vegetable is constantly engaged in raising its component materials from a lower plane to the higher, the animal, whilst raising one portion of these to a still higher level by the descent of another portion to a lower, ultimately lets down the whole of what the plant had raised; in so doing, however, giving back to the universe, in the form of heat and motion, the equivalent of the light and heat which the plant had taken from it."
Thus, as Tyndall later wrote: "As experimental contributors, Rumford, Davy, Faraday and Joule stand prominently forward; as theoretic writers (placing them alphabetically) we have Clausius, Helmholtz, Kirchoff, Mayer, Rankine, Thomson," and he distinguishes sharply between the two classes, as the world of science always must, without denying to either credit for that practical genius which makes the work of the one party useful or for that genius of foresight and insight which often leads the other far in advance of the investigator, giving quantitative values to relations thus earlier recognized.
Thus, also, the ideas now taking expression as scientific statements of nature's laws originated in a distant age, grew into form with experience and observation and restricted experimental research, until, with the opening of the XIXth century, and with the enormous development of scientific method and of experimental systems, and with the production in marvelous exactness and perfection of every form of instrument of research, quantities came to be exactly measured and the law of persistence of energy could be stated positively and quantitatively.
When the idea of equivalence of thermal and dynamic energies and of the formation of a thermodynamic science had come to be familiar to the leaders of scientific thought, the extension of the idea to embrace all the physical forces and energies was a simple and inevitable matter. The comprehension of all physical energies within the stated law naturally and promptly, and just as inevitably, led to the suggestion of the extension of the law to the so-called vital energies and forces and to its enunciation in that general form which permitted its application by Carpenter to the vital forces and its introduction by the biologists into their department of life and work. It was in the extension of such apparently obvious deductions to the seeming limit, and without a thought of the fact having originality at the time, that the writer, in the Vice-President's address before the American Association for the Advancement of Science, at St. Louis, in 1878, made that extension in an enunciation of the principle now called by Haeckel the 'Law of Substance.'[1] The de-
- ↑ At that time there were two Vice-Presidents in the organization of that Association, both of whom were expected, annually, to present addresses before the whole Association at special meetings held for that purpose.
