XX. 



RUDOLF JULIUS EMANUEL CLAUSIUS. 



[Proceedings of the American Academy, new series, vol. XVI, pp. 458-465, 1889.] 



RUDOLF JULIUS EMANUEL CLAUSIUS was born at Coslin in Pomer- 

 ania, January 2, 1822. His studies, after 1840, were pursued at Berlin, 

 where he became Privat-docent in the University, and Instructor in 

 Physics in the School of Artillery. He was Professor of Physics 

 at Zurich in the Polytechnicum (1855-67) and in the University 

 (1857-67), at Wiirzburg (1867-69), and finally at Bonn (1869-88), 

 where he died on the 24th of August, 1888. 



His literary activity commenced in 1847, with the publication of 

 a memoir in Crelle's Journal, "Ueber die Lichtzerstreuung in der 

 Atmosphare, und iiber die Intensitat des durch die Atmosphare 

 reflectirten Sonnenlichts."* This was immediately followed by other 

 writings relating to the same subject, two of which were subsequently 

 translated from Poggendorff's Annalen^f for Taylor's Scientific 

 Memoirs. A treatise entitled " Die Lichterscheinungen der Atmo- 

 sphare " formed part of Grunert's " Beitrage zur meteorologischen 

 Optik." 



An entirely different subject, the elasticity of solids, was discussed 

 in his paper (1849), " Ueber die Veranderungen, welche in den bisher 

 gebrauchlichen Formeln fur das Gleichgewicht und die Bewegung fester 

 Korper durch neuere Beobachtungen nothwendig geworden sind." { 



But it was with questions of quite another order of magnitude that 

 his name was destined to be associated. The fundamental questions 

 concerning the relation of heat to mechanical effect, which had been 

 raised by Rumford, Carnot, and others, to meet with little response, 

 were now everywhere pressing to the front. 



"For more than twelve years," said Regnault in 1853, "I have 

 been engaged in collecting the materials for the solution of this ques- 

 tion : Given a certain quantity of heat, what is, theoretically, the 

 amount of mechanical effect which can be obtained by applying the 

 heat to evaporation, or the expansion of elastic fluids, in the various 

 circumstances which can be realised in practice ? " The twenty-first 



* Vol. xxxiv, p. 122, and vol. xxxvi, p. 185. + Vol. Ixxvi, pp. 161 and 188. 



$ Pogg. Ann., vol. Ixxvi, p. 46 (1849). Comptes Rendus, vol. xxxvi, p. 676. 



