0'48 



EXPERIMENTS RELATIVE TO PHYSICAL OPTICJ. 



equally liable to the general law, which is the 

 principal subject of this paper. If we had 

 thermometers sufficiently delicate, it is pro- 

 bable that we might acquire, by similar 

 means, information still more interesting. 



with respect to the rays of invisible heat 

 discovered by Dr. Herschel ; but at present 

 there is great reason to doubt of the practi- 

 cabiUty of such an experiment. 



