AN INQUIRY 



CONCERNING THE 



CHEMICAL PROPERTIES THAT HAVE BEEN 

 ATTRIBUTED TO LIGHT. 



IN the second part of my Seventh Essay (on the 

 Propagation of Heat in Fluids) I have mentioned 

 the reasons which had induced me to doubt of the 

 existence of those chemical properties in light that 

 have been attributed to it, and to conclude that all 

 those visible changes which are produced in bodies by 

 exposure to the action of the sun's rays are effected, 

 not by any chemical combination of the matter of light 

 with such bodies, but merely by the heat which is gen- 

 erated or excited by the light that is absorbed by 

 them. 



As the decision of this question is a matter of great 

 importance to the advancement of science, and par- 

 ticularly to chemistry, and as the subject is in many 

 respects curious and interesting, it has often employed 

 my thoughts in my leisure hours ; and I have spent 

 much time in endeavouring to contrive experiments, 

 from the unequivocal results of which the truth might 

 be made to appear. Though I have not been so suc- 

 cessful in these investigations as I could wish, yet I 

 cannot help flattering myself that an account of the 

 results of some of my late experiments will be thought 



