H. V. Gill — Theory of Singing Flames. 189 



We have made experiments analogous to those described in 

 the case of the singing ilame to determine the manner in which 

 the note begins. Our experiments lead to the conclusion that 

 it is the same as in that case, and that the original note caused 

 by the draught is strengthened by the reactions we have de- 

 tailed. As the arguments used in the case of the singing 

 flame apply with even greater force in the present case, it is not 

 necessary to repeat them. 



III. 



There is, finally, one other case of a note caused by a flame 

 which we shall consider very briefly. An experiment was sug- 

 gested to test the theory in which the singing flame is explained 

 as if it were a heated body. If so, a taper flame ought to sing 

 if placed in a favorable position. An ordinary taper flame 

 remains perfectly silent. On dividing up the wick so that the 

 head of the taper stretched over the tube, a note was produced 

 which lasted several minutes. This is merely a case of Rijke's 

 experiment of the heated gauze above alluded to. Bijke's 

 experiment has been explained already, and is easily under- 

 stood if we consider the action of the pressure and various air 

 currents in a sounding pipe, and bear in mind that the most 

 favorable moment for the air to receive an increase of tempera- 

 ture is when a condensation is changing into a rarefaction. 

 The following passage from a lecture by Lord Rayleigh will 

 make this clear (" Nature," vol. xviii, p. 320, 1878) : " Perhaps 

 the easiest way to trace the mode of action is to begin with 

 the case of a simple vibration without a steady current (i. e. 

 the draught). Under these circumstances the whole of the air 

 which comes in contact with the metal in the course of a com- 

 plete period becomes heated ; and after this state of things 

 there is comparatively little further transfer of heat. The 

 effect of superposing a small steady upward current is now 

 easily recognized. At the limit of the inward motion, i. e., at 

 the phase of greatest condensation, a small quantity of air 

 comes in contact with the metal which has not done so before, 

 and is accordingly cool ; and the heat communicated to this 

 quantity of air acts in the most favorable manner for the 

 maintenance of the vibration." " Both in Kijke's and Bless'* 

 experiments the variable transfer of heat depends on the motion 

 of vibration, while the effect of the transfer depends upon the 

 variation of pressure. The gauze must therefore be placed 

 where both effects are sensible, i. e. neither near a node nor 

 near a loop." (We have found the same in the case of the 



* Riess's experiment consists of a note produced by a current of hot air passing 

 through a cool gauze. 



