ON THE PHYSICAL VIEW OF NATURE. 



109 



numerical estimate as between mechanical energy on 

 the one side, and the amount of one of the imponder- 

 ables i.e., heat as measured by the thermometer on 

 the other. Although his methods were not free from 

 objection, 1 while his arguments were mixed up with 



Mayer, 1842. His determinat on 

 is contained in his first paper, pub- 

 lished, as was Mohr's, in Liebig's 

 'Annalen' (vol. xlii., May), with 

 the title " Bemerkungen uber die 

 Kraf te der unbelebten Natur." The 

 experiments performed by Rumford 

 in 1798 were made the basis of a 

 calculation of the heat equivalent, 

 i.e., of the weight which can be 

 lifted one foot if the heat required 

 to raise a pound of water 1 be con- 

 verted into work against gravita- 

 tion, and the figure turns out to 

 be 1034 Ib. as compared with 772 

 Ib. given by Joule himself ( ' Phil. 

 Trans. ,' 1850 ; ' Joule's Papers,' vol. 

 i. p. 299). The earlier computations 

 of Seguin, based upon the work done 

 by the expansion of steam, were 

 referred to by Joule, Tyndall, and 

 Tait in 1862 and 1864 (' Phil. Mag.,' 

 4th series, vols. xxiv. and xxviii. ), and 

 shown to lead to figures further off 

 the mark than those of Mayer. In 

 the course of this later controversy 

 it became for the first time gen- 

 erally known that A. Colding, an 

 engineer in Copenhagen, had a 

 little later than Mayer (1843), and 

 almost simultaneously with Joule, 

 given a determination of the equiva- 

 lent based upon friction of metals, 

 which was lower than Mayer's. He 

 accordingly now figures as second 

 in Helm's list. One of Joule's 

 earliest experiments with heat, 

 4 ' evolved by the passage of water 

 through narrow tubes," gave the 

 equivalent as 770, very near the 

 figure, viz., 772, finally settled on 

 as correct in 1850. 



1 The reasoning of Mayer is not 

 completely contained in his first 



paper, which subsequently, on a 

 suggestion of Joule's appeared 

 in translation in the ' Phil. Mag. ' 

 (4th series, vol. xxiv. pp. 123, and 

 371 sqq.) The assumption (called 

 by Thomson in 1851 "Mayer's 

 hypothesis," see ' Math, and Phys. 

 Papers,' vol. i. p. 213) that "the 

 work spent in the compression of 

 a gas ... is exactly the mechani- 

 cal equivalent of the . . . heat 

 evolved," which Joule did not think 

 it right to accept without satisfying 

 himself by experiments (see ' Phil. 

 Mag.,' 4th series, vol. xxiv. p. 122), 

 was based by Mayer on an almost 

 forgotten experiment of Gay 

 Lussac's in the year 1807, as is evi- 

 dent from his subsequent paper, 

 published in 1845 (reprint in 

 ' Mechanik der Warme,' ed. Wey- 

 rauch, 1893, p. 53), and still more 

 from his correspondence with Baur 

 previous to his first publication 

 (ibid., p. 20, and 'Mayer's Briefe,' 

 p. 130, September 1841). The sub- 

 ject was exhaustively investigated 

 by Thomson and Joule in a joint- 

 memoir on " the thermal effects of 

 fluids in motion," 1852 (reprinted 

 both in Joule's and Lord Kelvin's 

 Scientific Papers), when it was 

 shown that for air Mayer's hy- 

 pothesis was approximately, but 

 not absolutely, correct. So long, 

 therefore, as the history of Mayer's 

 reasoning was not completely 

 known, it appeared as if he had 

 by a kind of accident hit upon an 

 approximately correct figure. See 

 Tait, 'Recent Advances' (3rd ed., 

 p. 53 ; but also Helm, 'Energetik,' 

 p. 24, and Mach, ' Warmelehre,' 

 p. 249). 



