GIBBS' PAPERS I AND II 53 



the grandest generalization of physical science, the Conservation of 

 Energy. The results of observation and calculation agree, whenever a 

 comparison is practicable, if the calculation is made upon the assump- 

 tion that the totality of energy in a system, potential as well as dynam- 

 ical, is as unchangeable as the totality of matter. This sweeping gen- 

 eralization includes and interprets Grove's experimental demonstration 

 of the correlation and convertibility of the different forms of energy, 

 known under the familiar names of gravity, elasticity, light, heat, elec- 

 tricity, magnetism, and chemical affinities. The conversion of heat 

 (which is supplied to an indefinite amount by the consumption of the 

 forests and the coal-beds) into ordinary mechanical energy or work, is 

 of the highest significance to the advancing civilization of the race; but 

 heat cannot be transformed into work without the transformation of a 

 larger amount of heat of high temperature into heat of low temperature. 

 This passage of heat from hot to cold bodies, without doing work, rein- 

 forced by the conduction and radiation of heat, creates the tendency to 

 what is now called the dissipation of heat. This is what the writer in 

 the London Spectator meant when he called hSat the communist of the 

 universe, the final consummation of this dissipation being a second 

 chaos. Sir William Thomson has computed that the sun has lost 

 through its radiations hundreds of times as much mechanical energy 

 as is represented by the motions of all the planets. The energy thus 

 dispensed to the solar system, and from it to remoter space, 'is dissi- 

 pated, always more and more widely, through endless space, and never 

 has been, and probably never can be, restored to the sun without acts 

 as much beyond the scope of human intelligence as a creation or anni- 

 hilation of energy, or of matter itself, would be.' Therefore, unless the 

 sun has foreign supplies, in the fall of meteors or otherwise, where its 

 drafts will be honored, its days are numbered. 



"What I have attempted to state in language as little technical as 

 possible is tersely expressed by Clausius in two short sentences: 'The 

 energy of the world is constant.' 'The entropy of the world (that is the 

 energy not available for work) tends constantly towards a maximum.' 



"Professor J. Willard Gibbs takes his departure from these two 

 propositions when he enters upon his investigation on the 'Equilibrium 

 of Heterogeneous Substances.' Any adequate theoretical treatment 

 of this complex subject must be, necessarily, highly mathematical, and 

 intelligible only to those familiar with the analytical theory of heat. 

 To assist the imagination, Professor Gibbs has devised various geomet- 

 rical constructions; especially one, of a curved surface, in which each 

 point represents, through its three rectangular coordinates, the volume, 

 energy, and entropy of a body in one of its momentary conditions. 



