MEMOIR XXX.] ON BURNING GLASSES AND MIRRORS. 437 



prosecution of them to a more favorable opportunity. 

 Obtaining from time to time several isolated facts, I was 

 led, in meditating upon them, to what seemed to be some 

 general conclusions respecting the chemical action of ra- 

 diations. Several of these were published, in a desultory 

 manner, in various periodicals ; but it was not until May, 

 1851, that they were collected in the Philosophical Mag- 

 azine, under the title of a " Memoir on the Chemical Ac- 

 tion of Light." Of this, the following is an abstract. 



The general discussion of the problem of the chemical 

 action of a ray involves the following considerations : 



1. In what manner does the ray act, and what are the 

 changes it undergoes ? 



2. What is the nature of the impression made on the 

 material group, the decomposition of which ensues ? 



Many facts justify the supposition that the parts of all 

 material substances are in a state of incessant vibration. 

 To each particular thermometric degree there belongs a 

 particular frequency of vibration. As soon as these mo- 

 tions approach four hundred billions in a second, red 

 light is emitted, and the temperature is near 1000 Fahr. 

 As the frequency increases, rays of a higher refrangibility 

 are in succession evolved, and the temperature correspond- 

 ingly rises. On the other hand, when these oscillatory 

 movements decline, the temperature of the body falls. 



These principles lead to a ready explanation of the 

 nature of the exchanges of heat and the cause of the 

 equilibrium of temperature. The vibratory molecular 

 motions are necessarily propagated to the ether, through 

 which medium they are again transferred to the particles 

 of other bodies, on which the ethereal waves impinge, as 

 a vibrating string excites undulations in the air, and 

 these, in their turn, can give birth to analogous motions 

 in other strings at a distance. 



There is an analogy between the relations of a hot 



