12 HIS TORT of the SOCIETK 



them by contad^. The thermometer, therefore, that is placed 

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

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

 focus of the other. If that body be copied 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 contacft, fupply the deficiency. 

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

 ved by future obfervatlons, than as a theory already eftablifli- 

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

 indeed diffictilt 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 juflice to the accvi- 

 racy and judgment with which they have condu(5led their in- 

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

 TET were again dire(5led toward this object. 



By the preceding inquiry, Dr Hutton was led to confider 

 the conne(5lion between light and fire, as well as between light 

 and heat ; a fubjev5l which he had formerly treated of in feve- 

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

 bliihed in his chemical diflertations. 



In thefe he objeded to the theory of fire as laid down by M, 

 LAvoisiE:^., and the French chemifts ; acknowledging, at the 

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

 j-anked among the greateft difcoveries in phyfics. It is a difcor- 

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

 the phenomena of burning, by which the exigence of fome 

 Other caufe is clearly pointed out, belide the decompofition of 

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

 which maintained- the air in a ftate of fluidity. The arguments 

 ipL fupport of this affertion, which Dr Hutton employs here, 

 a^e founded, on the appearances e^hibi-t^ by bodies, burning 



without 



