THE LAW OF SUBSTANCE. 473 



"But there is this marked contrast between the two kingdoms of or- 

 ganic nature in their material and dynamic relations to the inor- 

 ganic 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, Rum- 

 ford, Davy, Faraday and Joule stand prominently forward; as theoretic 

 writers (placing them alphabetically) we have Clausius, Helmholtz, Kir- 

 choff, 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 experi- 

 ence and observation and restricted experimental research, until, with 

 the opening of the XlXth century, and with the enormous development 

 of scientific method and of experimental systems, and with the produc- 

 tion in marvelous exactness and perfection of every form of instrument 

 of research, quantities came to be exactly measured and the law of per- 

 sistence 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 natu- 

 rally and promptly, and just as inevitably, led to the suggestion of the ex- 

 tension of the law to the so-called vital energies and forces and to its 

 enunciation in that general form which permitted its application by Car- 

 penter to the vital forces and its introduction by the biologists into their 

 department of life and work. It was in the extension of such appar- 

 ently obvious deductions to the seeming limit, and without a thought of 

 the fact having originality at the time, that the writer, in the Vice-Presi- 

 dent'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.'* 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. 



