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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 Cöslin, Pomerania, January 12, 1823, 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 mathematical 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 contributions of scientific papers to Poggendorff's "Annalen," some of the earliest of which were selected for translation in the first volume of Taylor's "Scientific Memoirs." In 1857 he was appointed by the Swiss Federal Government Professor of Natural Philosophy 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 afterward 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 suggestive 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