42 PHYSICS 



Thermodynamics 



Thermodynamics, as has been stated, in a singularly fruitful way 

 interpreted and broadened the old Leibnitzian principle of vis viva 

 of 1686. Beginning with the incidental experiments of Rumford 

 (1798) and of Davy (1799) just antedating the century, the new 

 conception almost leaped into being when J. R. Mayer (1842, 1845) 

 defined and computed the mechanical equivalent of heat, and when 

 Joule (1843, 1845, et seq.} made that series of precise and judiciously 

 varied measurements which mark an epoch. Shortly after Helmholtz 

 (1847), transcending the mere bounds of heat, carried the doctrine 

 of the conservation of energy throughout the whole of physics. 



Earlier in the century Carnot (1824), stimulated by the growing 

 importance of the steam engine of Watt (1763, et seq.), which Fulton 

 (1806) had already applied to transportation by water and which 

 Stephenson (1829) soon after applied to transportation by land, 

 invented the reversible thermodynamic cycle. This cycle or sequence 

 of states of equilibrium of two bodies in mutual action is, perhaps, 

 without a parallel in the prolific fruitfulness of its contributions to 

 modern physics. Its continued use in fifty years of research has 

 but sharpened its logical edge. Carnot deduced the startling doc- 

 trine of a temperature criterion for the efficiency of engines. Clapey- 

 ron (1834) then gave the geometrical method of representation 

 universally used in thermodynamic discussions to-day, though often 

 made more flexible by new coordinates as suggested by Gibbs (1873). 



To bring the ideas of Carnot into harmony with the first law of 

 thermodynamics it is necessary to define the value of a transform- 

 ation, and this was the great work of Clausius (1850), followed very 

 closely by Kelvin (1851) and more hypothetically by Rankine (1851). 

 The latter's broad treatment of energetics (1855) antedates many 

 recent discussions. As early as 1858 Kirchhoff investigated the 

 solution of solids and of gases thermodynamically, introducing at 

 the same time an original method of treatment. 



The second law was not generally accepted without grave mis- 

 giving. Clausius, indeed, succeeded in surmounting most of the 

 objections, even those contained in theoretically delicate problems 

 associated with radiation. Nevertheless, the confusion raised by the 

 invocation of Maxwell's " demon " has never quite been calmed; and 

 while Boltzmann (1877, 1878) refers to the second law as a case of 

 probability, Helmholtz (1882) admits that the law is an expression 

 of our inability to deal with the individual atom. Irreversible pro- 

 cesses as yet lie quite beyond the pale of thermodynamics. For these 

 the famous inequality of Clausius is the only refuge. The value of an 

 uncompensated transformation is always positive. 



The invention of mechanical systems which more or less fully 



