Prof. Tyndall on Sounding and Sensitive Flames. 97 



issuing from a single circular orifice in a common iron nipple. 

 I whistle, clap my hand, strike the anvil, and produce other 

 sounds; the flame is perfectly steady. Observe the gradual 

 change from this apathy to sensitiveness. The flame is now 

 4 inches high. I make its height 6 inches ; it is still indifferent. 

 I make it 10 inches ; a barely perceptible quiver responds to the 

 whistle. I make it 14 inches high, and now it jumps briskly 

 the moment the anvil is tapped or the whistle sounded. I aug- 

 ment the pressure; the flame is now 16 inches long, and you 

 observe a quivering which announces that the flame is near 

 roaring. I increase the pressure ; it now roars, and shortens at 

 the same time to a height of 8 inches. I diminish the pressure 

 a little ; the flame is again 16 inches long, but it is on the 

 point of roaring. It stands, as it were, on the brink of a pre- 

 cipice. The whistle pushes it over. Observe it shortens when 

 the whistle sounds, exactly as it did when the pressure was in 

 excess. The sonorous pulses, in fact, furnish the supplement 

 of energy necessary to produce the roar and shorten the flame. 

 This is the simple philosophy of all these sensitive flames. 



The pitch of the note chosen to push the flame over the 

 brink is not a matter of indifference. I have here a tuning- 

 fork which vibrates 256 times in a second, emitting a clear and 

 forcible note. It has no effect upon this flame. Here are three 

 other forks, vibrating respectively 320, 384, and 512 times in 

 a second. Not one of them produces the slightest impression 

 upon the flame. But, besides their fundamental notes, these 

 forks can be caused to sound a series of overnotes of very high 

 pitch. I sound this series of notes : the vibrations are now 

 1600, 2000, 2400, and 3200 per second respectively. The 

 flame jumps in response to each of these notes, the response to 

 the highest note of the series being the most prompt and ener- 

 getic of all. 



To the tap of a hammer upon a board the flame responds; 

 but to the tap of the same hammer upon an anvil the response 

 is much more brisk and animated. The reason is, that the 

 clang of the anvil is rich in the higher tones to which the flame 

 is most sensitive. 



Here again is an inverted bell, which I cause to sound by 

 means of a fiddle-bow, producing a powerful tone. The flame 

 is unmoved. I bring a halfpenny into contact with the sur- 

 face of the bell : the consequent rattle contains the high notes 

 to which the flame is sensitive. It instantly shortens, flutters, 

 and roars when the coin touches the bell. 



Here is another flame, 20 inches long. I take this fiddle in 

 my hand, and pass a bow over the three strings which emit the 

 deepest notes. There is no response on the part of the flame. 



Phil. Mag. S. 4. Vol. 33. No. 221. Feb. 1867. H 



