206 Manner in which Natural Bodies exhibit Colours. 



principles, that black objects must be considered as those 

 which absorb the light, and cipable of depriving it of its 

 luminous property : on the other hand, those must be con- 

 sidered as wiiile or colourless objects which reflect the light 

 that fails upon them, and for this reason appear white. 



But here arises another question — If daik objects destroy 

 the action of the light which falls upon thein, while white 

 objects do not, what is the efficient cause of this difterence ? 

 This question mav be easilv answered on the principles of 

 Newton .by this observation, that black objects absorb the 

 light, and white reflect it. 



This explanation, however, is merely an auxiliary hypo- 

 thesis to attempt to explain something, but it by no means 

 explains the result. Shuuld it be explained on satisfactory 

 grounds, a second question will aris-i, namelv, Why is light 

 absorbed by black objects, and n;.t by white ? Is this effect 

 accompanied by particular phaenomena^or not ? And if tiiis 

 be the case. What are the phsenomena which are exhibited 

 for our observation ? 



If the above experiments be made the ground for an ex- 

 planation of this point, it thence follows, that in the mo- 

 ment when light is deranged in its luminous action by a 

 black object, an exaltation of its temperature takes place. 



But the exaltation of the temperature of a body supposes 

 the exist'.'nce of free heat. If bodies, however, in a state 

 of rest, exposed to the action of light, can on no good 

 grounds be considered as capable of themselves to extricate 

 heat ; and if heat is produced by their contact with the rays 

 of light which are not hot of themselves, light must be con- 

 sidered as t'aat object which contains the principles sufficient 

 for the disengagement of heat. 



But if the heat combined with light cannot exercise an 

 action till the light is brought into contact with another 

 object, it must be combined with it in a different form. 

 This union or mixture of two heterogeneous bodies in a 

 new product supposes an affinity between them ; and this 

 is a suffiicir.nt proof that light must be considered as the 

 product of the mixture of caloric and another substance, 

 which unite by the power of affinity. 



We hence see by what means light, in consequence of 

 Its action on some bodies, can produce heat, and why this 

 is not the case with others. If an object, therefore, is ca- 

 pable of exciting heat by its contact with light, its attrac- 

 tive power for the matter that produces light must be greater 

 than the attractive power of this matter for caloric. Hence 

 it follows, that the productive matter of light is miscible with 



other 



