A MEASURE OF THEIR CONSTITUENT CALORIC. 87 



inflammable bodies, the power of refracting light 

 is two or three times greater, in respect to their 

 densities, than in salts, rocks, or any other stony 

 concretes, which are less combustible : and as it 

 was higher in the diamond than in any other 

 body which he tried, he arrived at the conclusion 

 that it was a sulphureous or unctuous body co- 

 agulated, and would be found inflammable. 

 (Optics, Book ii. 24050.) 



That there is at least a nucleus of truth in this 

 hypothesis of Newton, would appear from the 

 numerous experiments of Brewster, Wollaston, 

 Biot, Arago, and Dulong, who have found that 

 in phosphorus and sulphur, as in all those bodies 

 which are composed chiefly of hydrogen and 

 carbon, with various proportions of oxygen and 

 nitrogen, the power of refracting light is much 

 greater in proportion to their specific gravities, 

 than^in any other bodies ; and we have the most 

 decisive proof that they contain proportionally 

 more caloric around their particles, as might 

 naturally have been inferred from all the phe- 

 nomena of their combustion, volatility, and ten- 

 dency to assume the gaseous state. But, so far 

 as I am informed, no one has attempted to ascer- 

 tain what relation exists between the latent caloric 

 of bodies and their refractive powers, except my 

 friend Mr. Dyer, whose views on the subject, if 

 ever carried out, have not been published. 



The most important experiments on the re- 

 fractive power of gaseous substances with which 



