n8 THE POPULAR SCIENCE MONTHLY. 



students of the nature of heat ; and France, because he completed a 

 work begun by her own Sadi Carnot, and because of a sentimental 

 affection to which she had already given a unique expression. 



Rudolf Julius Emanuel Clausius was born in Coslin, 

 Pomerania, January 12, 1822, and died in Bonn, August 24, 1888. 

 He began his course of studies at the gymnasium in Stettin, where 

 he made such marked progress as to attract the attention of his 

 teachers and secure for him an early transfer to the University of 

 Berlin. Here he evinced a predominant taste for the mathemat- 

 ical branches. He afterward went to the University of Halle, and 

 received its doctor's degree in 1848. He then won the position of 

 a Privat Docent at the University of Berlin, and a few months 

 afterward was appointed Instructor of Natural Philosophy in the 

 School of Artillery. At about this time he began his contribu- 

 tions of scientific papers to Poggendorff's "Annalen," some of 

 the earliest of which were selected for translation in the first vol- 

 ume of Taylor's " Scientific Memoirs." In 1857 he was appointed 

 by the Swiss Federal Government Professor of Natural Philoso- 

 phy in the Polytechnic School at Zurich. His career at this place 

 was distinguished by continued activity in his favorite fields of 

 research, besides which " he published some short papers on some 

 purely mathematical questions, suggested, however, by physical 

 problems, and some papers dealing with what is generally known 

 as physical chemistry." He gave up his chair in Zurich in 1867 

 to go to a similar position in Wurzburg, whence two years after- 

 ward he removed to become Professor of Natural Philosophy in 

 the University of Bonn. He became dean of this institution in 

 1874, and continued there till his death. 



The memoirs published by Clausius are estimated to number 

 more than a hundred. Seventy-seven are recorded on the lists of 

 the Royal Society up to 1873. Among his earlier papers the most 

 famous are those "On the Nature of those Constituents of the 

 Atmosphere by which the Reflection of the Light within it is 

 effected," and " On the Blue Color of the Sky, and on the Morning 

 and the Evening Red," which were published while he was in his 

 tutorship at Berlin. While at Zurich he published " The Influence 

 of Pressure on the Freezing-Point " ; " The Mechanical Equivalent 

 of an Electric Discharge, and the Heating of the Conducting Wire 

 which accompanies it " ; " Electrical Conduction in Electrolytes " ; 

 and " The Effect of Temperature on Electric Conductivity." In 

 1866 he published an important paper " On the Determination of the 

 Energy and Entropy of a Body," in which a very valuable and sug- 

 gestive conception was set forth. The idea of entropy, by which 

 term is designated the available energy of a system, or that which 

 can be converted into mechanical work, which he first conceived 

 in 1854, and which led him to some extremely general and bold 



