SENSITIVE FLAMES AS ILLUSTRATIVE OF 

 SYMPATHETIC VIBRATION. 



BY PEOFESSOE BAEEETT. 



THE subject assigned to me for the present lecture is 

 Sensitive Flames. I do not propose, however, to deal with 

 this subject exclusively, but rather to make it the goal 

 which we shall gradually approach. By this means I 

 think you will find that so far from being a strange and 

 isolated phenomenon, a sensitive flame is really a striking 

 illustration of a very widespread and important law 

 relating to the reception of vibratory energy. 



It will be instructive for us if we first regard the mode 

 of production of the energy of vibration, then how this 

 energy is communicated from one system of bodies to 

 another. The simplest mode of exciting vibratory motion 

 is that seen in the swinging of an ordinary pendulum. 

 The to-and-fro motion which you see there gives rise to 

 waves in the air of the simplest kind. In the case of the 

 pendulum we have the motion sustained by the action of 

 gravity ; but in the case of a tuning fork we have the 

 motion sustained by the elasticity of the metal. The 

 nature of the vibration is, however, the same in both cases. 

 The motion of the prongs of the fork to and fro is precisely 

 analogous to the motion of a pendulum swinging to and 

 fro. These are instances of the simplest form of vibratory 

 motion, namely, the vibration of a body sensibly as a whole. 



These vibratory motions generate simple wave-forms. 

 Such a motion may have a uniform rise and fall across the 

 line of rest. But there are other less simple modes of 



