502 Dr. J. R. Mayer on the Mechanical Equivalent of Heat. 



that we have established leads, then, bow to the conclusion that 

 the motion that disappears becomes heat, or, in other words, 

 that both objects bear to each other an invariable quantitative 

 relation. The proof of this conclusion by the method of experi- 

 ment, the establishment of it in all its details, the tracing of a 

 complete harmony subsisting between the laws of thought and 

 the objective world, is the most interesting, but at the same 

 time the most comprehensive problem that it is possible to find. 

 What I, with feeble powers and without any external support or 

 encouragement, have effected in this direction is truly little 

 enough ; but — ultra posse nemo obligatus. 



In the paper referred to (vol. xxiv. p. 375)1 have thus expressed 

 myself with regard to the genetic connexion of heat and moving 

 force : — 



"If it be now considered as established that in many cases 

 {exceptio confirmat regulain) no other effect of motion can be 

 traced except heat, and that no other cause than motion can be 

 found for the heat that is produced, we prefer the assumption 

 that heat proceeds from motion, to the assumption of a cause 

 without effect and of an effect without a cause, — just as the 

 chemist, instead of allowing oxygen and hydrogen to disappear 

 without further investigation, and water to be produced in some 

 inexplicable manner, establishes a connexion between oxygen 

 and hydrogen on the one hand and water on the other." 



From this point there is but one step to be made to the goal. 

 At page 376 it is said : " The solution of the equations subsist- 

 ing between falling-force [that is, the raising of weight] and 

 motion requires that the space fallen through in a given time, 

 e. g. the first second, should be experimentally determined ; in 

 like manner, the solution of the equations subsisting between 

 falling-force and motion on the one hand and heat on the other, 

 requires an answer to the question, How great is the quantity 

 of heat which corresponds to a given quantity of motion or falling- 

 force ? For instance, we must ascertain how high a given weight 

 requires to be raised above the ground in order that its falling- 

 force may be equivalent to the raising of the temperature of an 

 equal weight of water from 0° to 1° C. The attempt to show 

 that such an equation is the expression of a physical truth may 

 be regarded as the substance of the foregoing remarks. 



(t By applying the principles that have been set forth to the 

 relations subsisting between the temperature and the volume of 

 gases, we find that the sinking of a mercury column by which a 

 gas is compressed is equivalent to the quantity of heat set free 

 by the compression ; and hence it follows, the ratio between the 

 capacity for heat of air under constant pressure and its capacity 

 under constant volume being taken as =1'421, that the warm- 



