of the prismatic Colours to heat and illuminate Objects. 271 



of them may easily be found; and we cannot too minutely 

 enter into an analysis of light, which is the most subtle of all 

 the active principles that are concerned in the mechanism of 

 the operations of nature. A better acquaintance with it may 

 enable us to account for various facts that fall under our daily 

 observation, but which have hitherto remained unexplained. If 

 the power of heating, as we now see, be chiefly lodged in the 

 red-making rays, it accounts for the comfortable warmth that 

 is thrown out from a fire, when it is in the state of a red glow ; 

 and for the heat which is given by charcoal, coke, and balls of 

 small-coal mixed up with clay, used in hot-houses ; all which, 

 it is well known, throw out red light. It also explains the 

 reason why the yellow, green, blue, and purple flames of burn- 

 ing spirits mixed with salt, occasion so little heat that a hand 

 is not materially injured, when passed through their corusca- 

 tions. If the chemical properties of colours also, when ascer- 

 tained, should be such that an acid principle, for instance, which 

 has been ascribed to light in general, on account of its changing 

 the complexion of various substances exposed to it, may reside 

 only in one of the colours, while others may prove to be dif- 

 ferently invested, it will follow, that bodies may be variously 

 affected by light, according as they imbibe and retain, or transmit 

 and reflect, the different colours of which it is composed. 



Radiant Heat is of different Refrangibility. 



I must now remark, that my foregoing experiments ascertain 

 beyond a doubt, that radiant heat, as well as light, whether 

 they be the same or different agents, is not only refrangible, 



mdccc N n 



