13 HIS TORT of the SOCIETr. 



them by contacft. The thermometer, therefore, that is placed 

 in the focus of one of the mirrors, in the above experiment, 

 will be affeiled by any body whatfoever that is placed in the 

 focus of the other. If that body be cooled below the tempera- 

 ture of the furrounding bodies, lefs light will be irradiated from 

 it, and reflecfted on the thermometer ; the thermometer, there- 

 fore, will be depreffed, till the influx of heat from the air, or 

 other bodies with which it is in contacfl, fupply the deficiency. 

 This, however, is thrown out rather as a queftion to be refol- 

 ved by future obfervations, than as a theory already cftablifli- 

 cd. The experiments by which it mufl ftand or fall are not 

 indeed difficult to be imagined. They are however of extreme 

 delicacy in the performance ; and Dr Hutton, who, in differ- 

 ing from the philofophers of Geneva, does juftice to the accu- 

 racy and judgment with vvhich they have condudled their in- 

 quiries, exprelTes a wifh, that the fkill and ingenuity of M. Pic- 

 tilt were again diredted toward this objedl. 



By the preceding inquiry, Dr Hutton was led to confider 

 the connedlion between light and fire, as well as between light 

 and heat ; a fubjeift which he had formerly treated of in feve- 

 ral papers read before the Royal Society, and afterwards pu- 

 blifhed in his chemical difTertations, 



Jn thefe he objeded to the theory of fire as laid down by M. 

 Lavoisier, and the French chemifts ; acknowledging, at the 

 fame time, that the oxygenating of bodies, by vital air, is to be 

 ranked among the greateft difcoveries in phyfics. It is a difco^ 

 very, however, in his opinion, that will by no means explain all 

 the phenomena of burning, by which the exiftence of fome 

 Other caufe is cleai'ly pointed out, beiide the decompofition of 

 the vital air, and the extrication of the caloriqiie or latent heat^ 

 which maintained the air in a ftate of fluidity. The argum£nts 

 ip fupport of this afTertion, vvhich Dr Hutto^n employs here, 

 a^e founded on the appearances exhibited by bodies, burning 



without 



