Prof. Tyndall on Sounding and Sensitive Flames. 95 



such a silent flame by a pitch-pipe, by the siren, or by the human 

 voice. It is also possible to cause one flame to effect the mu- 

 sical ignition of another. 



The sound which starts the flame must be nearly in unison 

 with its own. Both flames must be so near unison as to pro- 

 duce distinct beats. 



A flame may be employed to detect sonorous vibrations in 

 air. 



Thus, in front of this resonant case, which supports a large 

 and powerful tuning-fork, I move this bright gas-flame to and 

 fro. A continuous band of light is produced, slightly indented 

 through the friction of the air. The fork is now sounded, and 

 instantly this band breaks up into a series of distinct images of 

 the flame. 



Approaching the same flame towards either end of one of our tin 

 tubes with the sounding flame within it, and causing it to move 

 to and fro, the sonorous vibrations also effect the breaking up 

 of the band of light into a chain of images. 



In this glass tube, 14 inches long, a flame is sounding : I 

 bring the flat flame of a fish-tail burner over the tube, the 

 broad side of the flame being at right angles to the axis of the 

 tube. The fish-tail flame instantly emits a musical note of the 

 same pitch as that of the singing flame, but of different quality. 

 Its sound is, in fact, that of a membrane, the part of which it 

 here plays. 



Against a broad batVwing flame I allow a sheet of air, 

 issuing from a thin slit, to impinge. A musical note is the 

 consequence. The note can be produced by air or by carbonic 

 acid ; but it is produced with greater force and purity by oxygen. 

 The pitch of the note depends on the distance of the slit from 

 the flame. 



Before you burns a bright candle-flame : I may shout, clap 

 my hands, sound this whistle, strike this anvil with a hammer, 

 or explode a mixture of oxygen and hydrogen ; though so- 

 norous waves pass in each case through the air, the candle is 

 absolutely insensible to the sound; there is no motion of the 

 flame. 



I now urge from this small blowpipe a narrow stream of air 

 through the flame of the candle, producing thereby an incipient 

 flutter, and reducing the brightness of the flame. I now sound 

 the whistle; the flame jumps visibly. Matters may be so ar- 

 ranged that when the whistle sounds the flame shall be either 

 almost restored to its pristine brightness, or the amount of light 

 it still possesses shall disappear. 



Before you now burns a bright flame from a fish-tail burner. 

 I mav, as before, shout, clap my hands, sound a whistle, or 



