worked from the theory of matter to the theory of the steam engine, 

 so in electromagnetism, he worked from the theory of electromagnetic 

 actions to the theory of its industrial application to dynamos. 



Clausius' first publications were concerned with the action of 

 atmospheric dupt on sunlight. This seems to have directed his 

 thoughts to molecular physics, which was indirectly the foundation of 

 his greatest work. Thermodynamics was the region he explored, and 

 his exploration was guided by his insight into molecular physics. 

 When Clausius was beginning his independent activity the investiga- 

 tions of Bumford, Davy, Mayer, Joule, and Helmholtz had conclusively 

 shown that heat could be produced from work, while the thermo- 

 dynamic speculations of Carnot, founded upon the assumed 

 indestructibility of caloric, were receiving every day additional con- 

 firmation. There was an obvious difficulty here of which Carnot 

 himself was doubtless aware. Of this difficulty, in 1849, Sir William 

 Thomson writes, that if we abandon Carnot's fundamental axiom " we 

 meet with innumerable other difficulties insuperable without further 

 investigation and an entire reconstruction of the theory of heat from 

 its foundations. It is, in reality, to experiment that we must look, 

 either for a verification of Carnot's axiom and an explanation of the 

 difficulty we have been considering, or for an entirely new basis of 

 the theory of heat." 



It was at this juncture that Clausius, without waiting for additional 

 experiments, read, in the Berlin Academy on the 18th February, 1850, 

 his paper, " Ueber die bewegende Kraft der Warme, und die Gesetze, 

 welche sich daraus fur die Warmelehre selbst ableiten lassen." 



Caruot had assumed that a heat engine gave out the same heat at 

 the lower temperature as it took in at the higher, and founded his 

 theory on this assumption and upon the impossibility of perpetual 

 motion. Clausius, in the first place, emphasised that the heat given 

 out must be less than the heat taken in by an amount equivalent to 

 the work done, that this was required by the First Law of Thermo- 

 dynamics, the equivalence of Heat and Work. Thus modified, 

 Carnot s theorems could no longer rely for their proof on the im- 

 possibility of perpetual motion, and it was Clausius' great discovery 

 to found Thermodynamics upon the New Second Law of Thermo- 

 dynamics, " That heat tends to flow of itself from hot to cold bodies." 

 On these foundations Clausius raised again the Theory of Thermo- 

 dynamics, and thenceforward there was no serious doubt as to its 

 security. Several different ways of stating the Second Law of 

 Thermodynamics have been advocated, and objections have been 

 raised to each of them. Of these things Clerk Maxwell writes that 

 Clausius " first stated the principle of Carnot in a manner consistent 

 with the trne theory of heat." Of the varieties of statement he writes :' 

 " By comparing together these statements the student will be able to 



