174 HEAT AS A MEASURABLE QUANTITY. 



regarded by the advanced school of natural philosophers 

 as the result of external motions of matter. Robert 

 Boyle, in the preface to his work " An Experimental 

 History of Cold," published in 1664, says : — " The subject I 

 have chosen is very noble and important ; for since Heatltas so 

 general an interest in the Production of Nature's Phenomena, 

 that (Motion excepted, of which it is a kind) there is scarce 

 anything in Nature whose efficiency is so great and so diffused, 

 it seems not likely that its antagonist, Cold, should be a des- 

 picable Quality!' Huygens also adopted views similar to 

 those of Hooke ; and these views seemed to be in a fair 

 way of general acceptance until the brilliancy of Newton's 

 mathematical discoveries diverted thought, and established 

 a school which accepted the corpuscular theory as proved, 

 rejecting the vibratory theory as unorthodox — not having 

 the sanction of their illustrious founder. Hooke's concrete 

 idea of heat as motion was thus dropped, and the vague 

 ideas of an igneous fluid revived ; but these were not 

 allowed to remain a mere matter of speculation. The not 

 indefinite hypothesis of heat as a material under the name 

 " phlogiston," was subjected to the test of explaining the 

 then known chemical actions during the first half of the 

 -eighteenth century, and held no inconsiderable place in 

 professorial lectures as late as those of Black. These tests 

 introduced the system of weighing and measuring in 

 chemistry, and amongst others of measuring heat by the 

 degree of temperature it would impart to a definite quantity 

 of water, — which was certainly the first and most important 

 step in the science of heat. Then followed, as a direct con- 

 sequence, Black's discovery, about 1762, of the disappear- 

 ance of definite quantities of heat during the changes of 

 state, fusion and evaporation, and the respective reappear- 



