98 Prof. Draper on the Phosphorescence of Bodies. 



effect, that as the \'iolet end produces phosphorescence and the 

 red extinguishes it, this is a proof of opposition of action. In 

 explaining this fact, M. E. Becquerel supposes the darkening 

 power of the red rays to be diie to the more rapid disengagement 

 of the phosphorescence by reason of the heat produced by those 

 rays, and that the apparent antagonization is not attributable to 

 the supei-position of vibi'atory movements of light-rays of differ- 

 ent frequency, but to the relations of caloric and light. The 

 force of this explanation, however, thsappears when it is un- 

 derstood that light and heat, the chemical and phosphorogenic 

 rays, are, according to the principles of this able experimenter, 

 all manifestations of the same agent. It avails us nothing to 

 say, that a want of phosphorescence at the less refrangible end 

 of the speetnim is due to the heat-giving powers of those rays, 

 when that very heat-giving power is, under the hypothesis, de- 

 pendent on their comparative rapidity of vibration. 



In the further explanation of phosphorescence, I abandon, 

 therefore, expressions derived from the material theory of light, 

 and present again the views alluded to in the letter in question, 

 to the effect, that whenever a rathation falls upon a surface of 

 any kind, 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 

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

 facts of the radiation of heat, and the theory of calorific exchanges; 

 it also offers an explanation of the connexion of the atomic 

 weights of bodies and their specific heats. It s;xggests, that all 

 cases of the decomposition of compound molecules under the 

 influence of a ray is owing to a want of consentaneousness in the 

 vibrations of the impinging ray, and those of the molecular 

 group, which, iinable to maintain itself, is broken down under the 

 periodic 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 b, the 

 theoiy of the exchanges of heat teaches that the temperature of 

 the latter will steadily rise until equilibrium takes place. The 

 molecules of a communicate their vibratoiy movement to the 

 aether, and this in its turn imparts an analogous movement to 

 the molecules of b. For as the jethercal medium is of vastly less 

 density than the vibrating molecules, each of their oscillations 

 will jiroduce in it a determinate wave, which is propagated 

 through it according to the ordinary laws of undulation, in such 

 a way that the aether would be in repose after the wave had 

 passed, were it not for the recurrence of the continuing vibration 

 of the molecules. At each vibration the molecules of a lose a 

 part of their vis viva, by the quantity they have communicated 



