RUDOLF CLAUSIUS {1822-1878) 

 WILLIAM THOMSON, LORD KELVIN {1824-1907) 



After the principle of the conservation of energy had been 

 recognised, and its Hmitless vaHdity had become increasingly 

 more evident, it became time to follow out further Carnot's 

 ideas concerning the effect of heat, in the direction in which 

 he himself was already pursuing them, as we have learned 

 much later from his posthumous papers. The prosecution 

 of this plan was for the most part the work of Clausius in 

 Germany and W. Thomson in England, though both of them 

 were the authors of other by no means unimportant achieve- 

 ments. Clausius, who was the older, was also the pioneer, 

 and Thomson immediately followed, and supplied a great 

 deal of additional matter, which extended to the most out-of- 

 the-way conclusions. It was the recognition of a new fun- 

 damental law relating to heat which was here the essential 

 step forward, cleared up Carnot's doubts, connected to- 

 gether into a single system older and more recent knowledge 

 of heat, and allowed many further conclusions to be drawn. 

 This new fundamental law introduced by Clausius is 

 called the second law of the mechanical theory of heat, or 

 thermo-dynamics, the first law being the energy principle. 

 The second law is also founded upon experience; but it was 

 not necessary, as William Thomson at first thought, to col- 

 lect further experience in order to arrive at a new point of 

 view. It is only necessary, as Clausius could show, to make 

 use of a law derived from existing experience, namely: 

 'that heat never passes of itself from a colder to a warmer 

 body.' The fact that this statement is correct is shown by all 

 transference ofh eat, by means of conduction, convection, or 

 radiation, not however without it being necessary to give to 

 the words 'of itself a particular suitable interpretation. This 

 law of experience can already be described as the second law 

 of the theory of heat; but it may also be given other forms, 



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