HEAT AN INDESTRUCTIBLE FLUID. 1 75 



ance of the same quantities of heat during the reverse 

 changes, freezing and condensation. Black called this heat, 

 which had disappeared to reappear when the action was 

 reversed, "latent heat," thereby implying that the heat 

 which had disappeared was still present in the matter. 

 This view which, though now known not to be necessarily 

 true, received general acceptance, and seemed to afford what 

 amounted to an indisputable proof of the indestructible or 

 material character of heat ; and, being advertised by the 

 inventions of Watt, met with general recognition. The 

 nature of heat, from being a subject of speculation, was thus 

 placed on what seemed to be a sound foundation as an 

 elastic fluid, which, besides being indestructible and un- 

 createable, was definitely measurable. From this time the 

 science of heat, both as to its agency in the various chemical 

 actions and as to the laws of its communication by radiation 

 and conduction, made steady progress. To emphasize the 

 greater definition and certainty of the new hypothesis, 

 Lavoisier and the French Academicians, in 1787, invented 

 the name " Calorique," by which to distinguish heat 

 as a quantity from the temperature and sensations with 

 which it is associated, and so introduced great simplification 

 in the science. This simple definition of heat, however 

 consistent it might be with its real mechanical nature, was 

 in the main accepted literally, and caused heat to be 

 regarded as material, and this view seems to have found 

 confirmation during the rapid advances of experimental 

 science, mostly chemistry, which were taking place. The 

 assumption that whatever heat reappeared or disappeared 

 had been or had become latent was so reasonable whenever 

 (as in most cases) the phenomenon was the result of some 

 physical or chemical changes, that the few and less interest- 



