SENSITIVE FLAMES, ETC. 197 



nature of the vibration can be investigated thus. If a 

 sensitive flame be put under the influence of sound, and 

 a mirror moved to-and-fro in front of it, we shall find the 

 flame exhibiting a state of vibration exactly analogous to 

 that of the sounding body itself. I will make a sibilant 

 sound, and you will see the vibration if I move the mirror 

 to and fro. This is a non-musical sound, but if I make a 

 musical sound such, for example, as that from this reed, a 

 sort of strained and intense divergence of the flame is pro- 

 duced, the vibration of which can be seen better in the 

 mirror. 



Now, other bodies besides flame exhibit this sensitive 

 state. Jets of air, rendered visible by smoke, are ex- 

 tremely sensitive to sound ; so much so that I have found 

 an almost inaudible sound, made at a distance of two or 

 three hundred feet from such a jet of air, is capable of 

 very considerably affecting the jet. In like manner jets 

 of water can be thrown into this sensitive condition. 

 Savart indeed long ago showed that jets of water could 

 be influenced by musical notes. 



Nor need we stop here. The radiant energy of heat and 

 light may produce changes in bodies, analogous to those 

 produced in flames by sound. It has even been suggested 

 that sun-spots those changes on the sun's surface which 

 appear to be somewhat connected with the approach of 

 certain planets, may be illustrations of these sensitive 

 flames, as it were, upon a large scale, that is to say, a state 

 of tottering equilibrium, wherein a very feeble agent, if of 

 the proper kind, may produce a profound change in the 

 aspect of a body. Again many present have probably 

 heard of those experiments which Professor Tyndall 

 has made lately, where a beam of light has been sent 

 through a tube containing the vapours of volatile liquids, 

 and where those vapours, acted on by certain rays, sud- 

 denly assumed strange fantastic shapes. Such a profound 

 change produced by the radiant energy of light is analo- 

 gous to the change produced in a flame by the sonorous 

 vibrations of the air. In both cases it is an instance of 

 sympathetic vibration or resonance. And it is not impos- 

 sible that living organisms, and even the mind of men, 

 may be found subsequently to be subject to a similar law ' } 

 but into this of course I have no right to enter here. 



