ON THE PHYSICAL VIEW OF NATLKE. 



109 



numerical estimate as between mechanical energj' on 

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

 ables — i.r., heat as measured by the thermometer — (jn 

 the other. Although his methods were not free from 

 objection/ while his arguments were mixed uj. with 



Mayer, 1S42. His deteriuiiiaiiuii 

 is contained in his first paper, pub- 

 lished, a^ was Mohrs, in Liebig's 

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

 the title " Bemerkungen iiber die 

 Krtif te der unbelebten Natur." The 

 experiments performed by Rumford 

 in 179S 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 lb. its compared with 772 

 lb. given by Joule himself (' Phil. 

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

 L p. 299). The earlier computations 

 of Seguin, based upon the work done 

 by the expansion of steam, were 

 referred to bv Joule, TvndaU, and 

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

 4th series, vols, xsiv.aud xxviii.),aud 

 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, 

 "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 18.50. 



' The reasoning of Mayer is not 

 completely contained in his first 



paper, which subsetjuently, on a 

 suggestion of Joule's, appeared 

 in translation in the ' Phil. Mag.' 

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

 371 sqq.) The assumption (calletl 

 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 nut 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 pajjer, 

 published in 1845 (reprint in 

 ' Mechanik der War me,' ed. Wey- 

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

 from his correspondence with Baur 

 previous to his first publication 

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

 p. 130, September 184 i). 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 Li>rd 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 

 rciisoning was not conij'letely 

 known, it appeared as if he bad 

 by a kind of accident hit upon an 

 approximately correct figure. See 

 Tait, 'Recent Advances' (3rd e<l., 

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

 p. 24, and Mach, ' Warmelehre,' 

 p. 249). 



