MOHR, COLDING, AND MAYER 211 



by a discussion of falling bodies, defined heat as Kraft and not as motion, 

 drew an analogy between compression of air and fall of bodies, and deduced 

 a value for the mechanical equivalent of heat on the assumption that the 

 heat generated in suddenly condensing a gas was equal to the work done 

 in condensation. Tait maintained that such a mingling of truth and error 

 could not be accepted as a sound basis for the true doctrine of thermodynamics ; 

 that it was doubtful if in any particular which could be accepted as sound 

 physics Mayer had anticipated others ; that his argument in regard to the 

 experiment of heating air by compression involved a gratuitous assumption 

 which might or might not be true ; and that already Joule, in his remarkable 

 experiments on the production of heat by electricity and friction (1840 to 

 1843), had in an irreproachable scientific manner elucidated the true nature 

 of heat. 



Mayer's later pamphlets of 1845 an ^ 1848 contained, as Tait pointed 

 out in the second chapter of his Thermodynamics, many beautiful examples 

 of the law of transformations. So also did Mohr's papers of 1837, Grove's 

 Correlation of the Physical Forces (1842), Joule's papers and lectures between 

 1840 and 1847, Colding's publications (1840) and Helmholtz's great memoir 

 of 1847. Indeed, as early as 1834, Mrs Somerville in her Connection of the 

 Physical Sciences, had called attention to the generality of such transformations. 

 In fact the notions of transformability and of the equivalence of heat and 

 work were in the air. The time at last was ripe for the full comprehension, 

 appreciation, and development of the much earlier experiments of Davy and 

 of Rumford. It is not surprising that several minds of the first order were 

 pondering over the significance of these and related phenomena, each 

 investigator approaching the subject in his own way and to a large extent 

 independent of the others. Yet by the great majority of their contem- 

 poraries the early work of these true philosophers was not fully appreciated. 

 Mohr's first paper, " Ueber die Natur der Warme," appeared in 1837 ' m 

 Liebig's Annalen (Vol. xxiv) ; but Poggendorf declined an expansion of 

 this paper, which was however accepted for publication in Baumgartner's 

 and v. Holger's Zeitschrift fur Physik, a publication of comparatively 

 limited circulation. Mayer's 1842 paper, " Bemerkungen iiber die Krafte 

 der unbelebten Natur," made its ddbut in Liebig's Annalen, just five years 

 later than Mohr's similar paper. Neither of them seems to have had any 

 traceable influence in moulding contemporary scientific thought. Helmholtz 

 apparently knew nothing of them when he wrote his tract in 1847; and 



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