98 Prof. Tyndall on Sounding and Sensitive Flames. 



I sound the highest string : the jet instantly squats down to a 

 tumultuous bushy flame, 8 inches long. I have here a small 

 bell, the hammer of which is caused to descend by clock-work. 

 I hold it at a distance of 20 yards from the flame. The strokes 

 follow each other in rhythmic succession, and at every stroke 

 the flame falls from a height of 20 to a height of 8 inches. 



The rapidity with which sound is propagated through air is 

 well illustrated by these experiments. There is no sensible inter- 

 val between the stroke of the bell and the shortening of the flame. 



Some of these flames are of marvellous sensibility ; one such 

 is at present burning before you. It is nearly 20 inches long; 

 but the slightest tap on a distant anvil knocks it down to 8. I 

 shake this bunch of keys or these few copper coins in my hand: 

 the flame responds to every tinkle. I may stand at a distance 

 of 20 yards from this flame : the dropping of a sixpence from a 

 height of a couple of inches into a hand already containing coin 

 knocks the flame down. I cannot walk across the floor without 

 affecting the flame. The creaking of my boots sets it in vio- 

 lent commotion. The crumpling of a bit of paper, or the 

 rustle of a silk dress, does the same. It is startled by the 

 plashing of a raindrop. I speak to the flame, repeating a few 

 lines of poetry; the flame jumps at intervals, apparently picking 

 certain sounds from my utterance to which it can respond, while 

 it is unaffected by others. 



In our experiments downstairs we have called this the vowel 

 flame, because the different vowel sounds affect it differently. 

 Vowel sounds of the same pitch are known to be readily distin- 

 guishable. Their qualities or clang-tints are different, though 

 they have a common fundamental tone. They differ from each 

 other through the admixture of higher tones with the funda- 

 mental. It is the presence of these higher tones in different 

 proportions that characterizes the vowel sounds ; and it is to these 

 same tones, and not to the fundamental one, that our flame is 

 sensitive. I utter a loud and sonorous U, the flame remains 

 steady ; I change the sound to 0, the flame quivers ; I sound E, 

 and now the flame is affected strongly. I utter the words boot, 

 boat, and beat in succession. To the first there is no response; 

 to the second, the flame starts ; but by the third it is thrown 

 into violent commotion ; the sound Ah ! is still more powerful. 

 When the vowel sounds are analyzed, their constituents are 

 found to vary in accordance with the foregoing experiments, 

 those characterized by the sharpest overtones being the most 

 powerful excitants of the flame. (See Helmholtz in Pogg, 

 Annalen, vol. cviii. p. 286.) 



The flame is peculiarly sensitive to the utterance of the letter 

 S. If the most distant person in the room were to favour me 

 with a " hiss," the flame would be instantly shivered into tu- 



