28 Britain's Heritage of Science 



Joule was, therefore, necessarily antagonistic to Carnot's 

 assumption. 



William Thomson (1824-1907), known to the present 

 generation as Lord Kelvin, while studying in Regnault's 

 laboratory in Paris, had become acquainted with the 

 important conclusions that may be drawn from Carnot's 

 thermodynamic cycle, and with the efforts which were being 

 made in France to verify the relations between the thermal 

 properties of substances which can be derived from it. 

 Though at first reluctant to abandon so fertile a principle, 

 and hesitating to give full assent to Joule's views, he soon 

 discovered that Carnot's reasoning may be modified so as to 

 bring it into harmony with the principle of the conservation 

 of energy. The same solution had occurred to Clausius, who, 

 anticipating Kelvin, was thus the first to give the correct 

 theory of the heat engine; but we are here concerned only 

 with the account of Kelvin's share in advancing the 

 subject; and a very magnificent share it was. His great 

 paper " On the Dynamical Theory of Heat," communicated 

 to the Royal Society of Edinburgh in 1851, places the whole 

 matter on a firm scientific basis, and establishes relations 

 between the physical properties of substances which have 

 all been verified experimentally. Full credit is given in 

 the paper to those who have contributed to, and, in part, 

 initiated, the ideas which led up to the final recognition 

 of the conservation of energy as the most fundamental 

 law of nature. What is called the second law of thermo- 

 dynamics is really the adaptation to thermodynamics 

 of the axiom expressing the impossibility of obtaining 

 a perpetual motion by a heat-engine. As formulated 

 by Lord Kelvin, it runs as follows : " It is impossible, 

 by means of inanimate material agency, to derive 

 mechanical effect from any portion of matter by cooling 

 it below the temperature of the coldest surrounding 

 objects." 



Considerations leading up to a complementary principle 

 as important as that of the conservation of energy seem to 

 have been in Kelvin's mind at an early stage. If we imagine 

 a hot and a cold body, say, the boiler and condenser of a 

 steam engine, we may, by transferring the heat from the 



