102 



SCIENTIFIC THOUGHT. 



by the school of which Laplace was the most distin- 

 guished representative, natural philosophers like Black,^ 

 Eumford, and Davy had approached the study of those 

 phenomena where heat and chendcal change are the 

 prominent features. The phenomena wdiich they 

 studied experimentally can be comprehended under the 

 head of the disappearance and appearance of heat as 

 measured by the thermometer, or as recognisable 

 directly by our sensation of heat. Black accounted 

 for the disappearance of heat by the doctrine of latent 

 heat, and measured this by the capacity ^ for heat, or 

 the specific heat of different substances. Eumford 

 made exact measurements of the heat generated by 

 friction, and showed that Black's doctrine of latent 

 heat did not account for it. Both Black and Eum- 

 ford were led to science from the side of practical in- 

 terests. Black, like Young after him, was a physician. 

 Eumford was all through his life occupied with the 



1 Joseph Black (1728-99), one of 

 the founders of chemistry, and a 

 prominent figure in that illustrious 

 circle of philosophers who, during 

 the second half of the eighteenth 

 century, made the literature and 

 science of Scotland renowned over 

 the whole world, published very 

 little, being mostly known througli 

 his teaching and his pupils. His 

 name is, even to the present day, 

 rarely to be found in French books ; 

 whereas in Germany, mainlj' owing 

 to the historical writings of Herr- 

 mann Kopp, and quite recently of 

 Prof. E. Mach, his great merit and 

 originality have been fully recog- 

 nised. See Kopp, ' Geschichte der 

 Chemie,' vol. i. p. 226, &c.; 'Die Ent- 

 wickelungder Chemie,' 1873, pp. 57, 

 &c., 88, &c. ; E. Mach, ' Die Prin- 

 cipien der Wiirmelehre,' 1896, p. 



156, &c. Black, who as early as 

 1755 had shown that carbonic acid 

 gas could disappear as a gas and 

 become "fixed," showed later 

 that heat could disappear as tem- 

 perature and become " latent." 

 By himself, indeed, the former 

 important discovery was not inter- 

 preted against the then i-eiguing 

 phlogistic theory, nor was the latter 

 used to upset the material theory 

 of heat. Now, however, both dis- 

 coveries are cornerstones in the 

 history of science. 



^ According to Dr Young (' Lec- 

 tures,' new ed., p. 499), the term 

 " capacity " is due to Dr Irvine, 

 who, as well as Dr Crawford, was 

 much influenced by Black's lec- 

 tures. These were first published 

 in 1802 by Robison, three years 

 after the author's death. 



