286 EVOLUTION, GENETICS, AND EUGENICS 



Newton's third law of the equality of action and reaction is the 

 foundation of the modern doctrine of energy, not only in the Newto- 

 nian sense but in the most general sense. Newton divined the prin- 

 ciple of the conservation of energy in mechanics; Rumford (1798) 

 maintained the universality of the laws of energy; Joule (1843) 

 estabUshed the particular principle of the conservation of energy, 

 namely the exact equivalence between the amount of heat produced 

 and the amount of mechanical energy destroyed; and Helmholtz, in 

 his great memoir Uber die Erhaltung der Kraft, extended this system 

 of conservation of energy throughout the whole range of natural 

 phenomena. A familiar instance of the so-called transformation of 

 znergy is where the sudden arrest of a cool but rapidly moving body 

 produces heat. This was developed as \.\ie first law of thermodynamics. 



At the same time there arose the distinction between potential 

 energy, which is stored away in some latent form or manner so that 

 it can be drawn upon for work — such energy being exemplified me- 

 chanically by the bent spring, chemically by gunpowder, and elec- 

 trically by a Leyden jar — and kinetic energy, the active energy of 

 motion and of heat. 



While all active mechanical energy or work may be converted 

 into an equivalent amount of heat, the opposite process of turning 

 heat into work involves more or less loss, dissipation, or degradation 

 of energy. This is known as the second law of thermodynamics and is 

 the outgrowth of a principle discovered by Sadi Carnot (1824) and 

 developed by Kelvin (1852, 1853). The far-reaching conception of 

 cyclic processes in energy enunciated in Kelvin's principle of the 

 dissipation of available energy puts a diminishing limit upon the 

 amount of heat energy available for mechanical purposes. The avail- 

 able kinetic energy of motion and of heat which we can turn into work 

 or mechanical effect is possessed by any system of two or more bodies 

 in virtue of the relative rates of motion of their parts, velocity being 

 essentially relative. 



These two great dynamical principles that ' the energy of motion 

 can be converted into an equivalent amount of heat, and that a certain 

 amount of heat can be converted into a more limited amount of power 

 were discovered through observations on the motions of larger masses 

 of matter, but they are beUeved to apply equally to such motions as 

 are involved in the smallest electrically charged atoms (ions) of the 

 chemical elements and the particles flying off in radiant energy as 

 phosphorescence. Such movements of infinitesimal particles underlie 



