i6' HIS TORT of the SOCIETT. 



liftent with the propagation of heat. Inftances, ftill more re- 

 markable, of the rapid progrefs of fire, are found in the inflam- 

 mation of fuch vapours, when mixed with that proportion of 

 vital air which is necefTary for decompofing the phlogiftic fub- 

 ftance. 



On the whole, Dr Hutton concludes, that in na cafe is the 

 light which appears in burning, an effecfl of the heat obtained 

 from the decomposition of vital air, but that it is the extrication 

 of phlo^ifton, of fixed light, or a certain modification of the fb- 

 lar fubflance, which had exifted in the inflammable bodies, and 

 had been chemically combined with their elements. It appears 

 alfo, that it is light which is immediately produced in burning, 

 and that it is only mediately that heat is excited : This is true 

 both of combuftible bodies which burn in an affociated ftate, 

 and of thofe inflammable fubftances where the emerging light 

 heats both the inflammable body, and the contiguous atmofphe- 

 ric fluid. 



The Docflor proceeds to explain, more at large, his notions 

 of the folar fubflance, of which he conceives light, heat, phlo- 

 gifton, and eledlricity, to be fo many different modifications. 

 His notions on this fubje(5l are very peculiar, as he conceives 

 the folar matter to be without gravitation, without inertia, and, 

 it may be added, without extenflon. The nature of this ab- 

 ftradl does not admit of entering further on the argument : It 

 is fufflcient to remark, that the theory of beat feems to be 

 arrived at a point where it mufi almofl unavoidably fland ftill, 

 till fome experiments fhall determine how far the gravitation of 

 bodies is affedted by the heat, whether fenfible or latent, that is 

 contained in them. The experiments already made, though 

 ingenioufly contrived, and ably executed, are not fufEcient to 

 decide a queftion of fuch extreme delicacy ; nor ' does it feem 

 probable, that, without having recourfe to the pendulum, a fa- 

 tisfadory folution of the difficulty will ever be obtained. 



