Mr. Talbot on the N } attire of Light. 115 



of several yards. In this experiment I have no means of 

 judging in what proportion the light was augmented, but con- 

 sidering the facts above stated, it could not have been less 

 than several hundred times*. 



I do not know whether the explanation which I am about 

 to offer of this phenomenon has ever been suggested, at any 

 rate I do not remember to have met with it, and therefore 

 I will mention it here briefly. All vibrating bodies communi- 

 cate their own motion to the elastic medium in which they vi- 

 brate. This is a purely mechanical effect. We see an ex- 

 ample of it in the atmosphere, which is set in motion by any 

 vibrating body. It is by no means necessary that there should 

 be any affinity between the air and the sonorous body, but 

 only that the latter should move with a certain degree of ra- 

 pidity and regularity. Now, suppose the velocity of vibration 

 increased to an immense degree : and there is no difficulty in 

 conceiving that the moving body may then become capable of 

 communicating its vibrations to the surrounding cether : in 

 which case it will cause the formation of waves of light, or, in 

 other words, it will become a luminous object. Indeed, it is 

 difficult to deny the theoretical possibility of such an occur- 

 rence, without at the same time refusing to the aether the or- 

 dinary qualities of an elastic medium, and thereby abandoning 

 all analogy between light and sound. But whether such a 

 production of light be practically possible depends on whether 

 the particles of ordinary matter are capable of executing vi- 

 brations with a rapidity at all comparable to those of light. 

 Mechanical means are evidently too rude for the production 

 of such an effect; but heat, considered as a disturbing cause 

 of molecular equilibrium, seems to be an agent of adequate 

 power and energy*. 



I am of opinion, therefore, that the emission of intense light 

 by a particle of lime in this experiment, without the loss of 

 any portion of its own substance, arises from the cause above 

 referred to, namely, that the heat throws the molecules of 

 lime into a state of such rapid vibration that they become 

 capable of influencing the surrounding aetherial medium, and 

 producing in it the undulations of light. 



§ 2. According to the above explanation, the heat of the 

 alcohol flame is only necessary in order to cause vibrations of 

 the molecules of the lime. If, therefore, any substance could 

 be found that would vibrate when cold, it might be capable 

 of emitting light spontaneously. This appears to me a 

 plausible explanation of what is commonly termed phospho- 

 rescence. Solar phosphori are those which, having been ex- 



[* See our " Scientific Intelligence and Miscellaneous Articles" in the 

 present Number. — Eoit.] 



Q2 



