MEMOIK IX.] EFFECT'S OF HEAT ON PHOSPHORESCENCE. 



that a want of phosphorescence at the less refrangible end 

 of the spectrum is due to the heat-giving powers of those 

 rays, when that very heat-giving power is under the hy- 

 pothesis dependent on their comparative rapidity of vi- 

 bration. 



We may, therefore, in the explanation of phosphor- 

 escence, abandon expressions derived from the material 

 theory of light, and assume that whenever a radiation 

 falls upon any surface, it throws the particles thereof 

 into a state of vibration, just as in the experiment of 

 Fracaster, in which a stretched string is made to vibrate 

 in sympathy with a distant sound, and yield harmonics, 

 and form nodes. Such a view includes at once the facts 

 of the radiation of heat and the theory of calorific ex- 

 changes ; it also offers an explanation of the connection 

 of the atomic weights of bodies and their specific heats. 

 It suggests that all cases of decomposition of compound 

 molecules under the influence of a radiation are owing 

 to a want of consentaneousness in the vibrations of the 

 impinging ray and those of the molecular group, which, 

 unable to maintain itself, is broken down under the pe- 

 riodic impulses it is receiving into other groups, which 

 can vibrate along with the ray. 



If a hot body, a, be placed in presence of a cold body, 

 >, the theory of the exchanges of heat teaches that the 

 temperature of the latter will steadily rise until equi- 

 librium between the two takes place. The molecules of 

 a communicate their vibratory movement to the ether, 

 and this in its turn imparts an analogous movement to 

 the molecules of b. For, as the ethereal medium is of 

 vastly less density than the vibrating molecules, each of 

 these oscillations will produce in it a determinate wave, 

 which is propagated through it according to the ordi- 

 nary laws of undulations, in such a way that the ether 

 would be in repose after the wave had passed, were it 



