JO SI AH WILLARD GIBBS 481 



edly of diagrams, immediately recognized the importance of this paper, 

 part of which he incorporated as a chapter in his " Theory of Heat,"*" 

 and, shortly before his death, he sent Gibbs a copy of a model of the 

 thermodynamic surface constructed to scale with his own hands.*^ 

 These solid diagrams have played a great part in the elaborate studies 

 of the continuity of gaseous and liquid states by Van der Waals and 

 his pupils, of which we have recently witnessed the final triumph in 

 the liquefaction of helium. 



During the years 1875-8, Gibbs published the work which is his 

 chief title to fame, his memoir " On the Equilibrium of Heterogeneous 

 Substances."*^ This treatise deals, as the title implies, with the statics 

 of chemical substances which, as gases, vapors, liquids or solids, are in 

 actual physical contact with each other, whether influenced or modified 

 by gravity, osmosis, catalysis, capillarity or electromotive force or exist- 

 ing under such varied aspects as gaseous mixtures, liquid films, " solid 

 solutions," or crystals. For the first time chemical substances are 

 treated as continuous or contiguous " phases " of " matter in mass '* 

 acted upon, like mechanical systems, by forces having " potentials " — 

 a new way of looking at things which has since become the definite 

 view-point of physical chemistry. As Larmor says, " Gibbs made a 

 clean sweep of the subject, and workers in the modern experimental 

 science of physical chemistry have returned to it again and again to 

 find their empirical principles forecasted in the light of pure theory, 

 and to derive fresh inspiration for new departures."*^ Some of its 

 theorems, as the Helmholtz doctrine of free energy,** Konowalow's 

 theorem of indifferent points,*^ Curie's theory of " crystal habit,"*' 

 were rediscovered by later investigators in ignorance of the earlier 

 work. Indeed the primary intention of Gibbs's memoir, to treat chem- 

 ical changes as a branch of mechanics, was not, at first, clearly under- 

 stood, the long deferred review in the " Fortschritte der Physik "" 

 merely listing its contents. Maxwell, however, with the same cordial 

 recognition which he had shown to Eowland, grasped its significance 

 at once, incorporated some of its results in his memoir on " Diflfu- 

 sion,"*^ and in an appreciative discourse before the Cambridge Philo- 



«> Maxwell, " Theory of Heat," London, 1902, 204-8. 



" " Copies of this model were distributed by Maxwell evidently with a cer- 

 tain amount of playful mystery, for each recipient thought that he was the 

 happy possessor of one of (at most) three. The writer knows of six at least, 

 and possibly there are more." C. G. K. in Nature, 1907, LXXXV., 361. 



"Tr, Connect. Acad., 1875-8, III., 108-248; 343-594. Abstract by Gibbs 

 in Am. J. Sc, 1878, 3. s., XVI., 441-458. 



"Larmor, " Encycl. Britan.," 10th ed., 1902, IV., 172. 



** Helmholtz, Sitzungsb. d. k. preuss. Akad. d. Wissetisch., XXII. 



"Konowalow, Wied. Ann., 1881, XIV., 48. 



« Curie, Bull. Soc. Min., 1885, VIII., 145. 



"Fortschr. d. Physik., 1878, XXXIV., 198. 



""Encycl. Britan.," 9th ed., VII., 214-21. 



