528 THE THEORY OF ENERGY AND THE LIVING WORLD. 



rendered valuable service. It lias inspired researches replete with 

 interest, and has renovated the appearance of certain branches of 

 physiology. 



It begins to have a place in the courses of higher instruction in the 

 universities of Germany, America, and France. M. Chauveau is the 

 foremost exponent of these new tendencies among us; his works and 

 those of his students form the most important contribution (of our time) 

 to the constitution of physiological energetics. 



ii. 



The doctrine of energy was first conceived in physiology before it 

 was taken up in the department of physics with such extraordinary 

 acceptation. Eobert Mayer was a naturalist and a physician. Helm- 

 holtz was a physiologist before he became a physicist. Both saw in 

 the new idea a powerful instrument for physiological investigation. 

 The publication in which Mayer set forth in 1845 his remarkable views 

 on the movements of organisms in their relation to nutrition and the 

 commentary of Helmholtz dispel all doubt in respect to their positions 

 in this regard. The " Remarks upon the mechanical equivalent of 

 heat" were published about six years after this first work. 



The doctrine of energy is in our day but returning to the science 

 which was its cradle. It returns, sanctioned by the demonstrations 

 of physics, as the most general doctrine which has ever been proposed 

 in natural philosophy, and is the one least weighted by hypotheses. 

 It reduces to two fundamental principles the multitude of minor prin- 

 ciples and the smaller number previously recognized as general which 

 had dominated the sciences of nature. It can be shown without great 

 difficulty that the principle of Robert Mayer, suitably extended, con- 

 tains the principle of the inertia of matter stated by Galileo and 

 Descartes; that of the quality of action and reaction ascribed to New- 

 ton; even that of the conservation of matter (or rather of mass) due to 

 Lavoisier, and finally the experimental law of equivalence which is 

 associated with the name of the distinguished English physicist Joule 

 and from which is derived the principle of Hess, and the principle of 

 •'initial and final states" of Berthelot. 



Similarly Carnot's principle, as extended in a large and comprehen- 

 sive fashion by contemporary theorists, such as William Thomson (Lord 

 Kelvin), Le Chatelier, and others, may be considered as the universal 

 law of mechanical, physical, and chemical equilibrium. It includes, as 

 G. Robin has shown, d'Alembert's principle of virtual velocities, and, 

 according to some physicists, the special laws of chemical and physico- 

 chemical equilibrium. 



These two principles, then, contain the essence of all natural sciences. 

 Since the true significance of these laws is to express the necessary 

 relations of all the phenomena of the universe, they impart a real 

 homogeneity to apparent diversity, and hence they may be made to 



