382 



Prof. Tyndall on the Action of Sonorous 



which is worked by clockwork. I send my Fii 



assistant to the most distant part of the gal- 

 lery, where he detaches the hammer. The 

 strokes follow each other in rhythmic suc- 

 cession, and at every stroke the flame falls 

 from a height of 20 to a height of 8 inches, 

 roaring as it falls. 



The rapidity with which sound is propa- 

 gated through aii* is well illustrated by these 

 experiments : there is no sensible interval 

 between the stroke of the bell and the duck- 

 ing of the flame. 



When the sound acting on the flame is of 

 very short duration, a curious and instructive 

 effect is observed. The sides of the flame 

 halfway dowm and lower are seen suddenly 

 fringed by luminous tongues, the central 

 flame remaining apparently undisturbed in 

 both height and thickness. The flame, 

 both in its normal state and with its fringes, 

 is shown in fig. 13. The effect is due to the 

 retention of the impression upon the retina. 

 The flame actually falls as low as the fringes, 

 but its recovery is so quick that to the eye 

 it does not appear to shorten at all*. 



The most marvellous flame hitherto discovered is now before 

 you. It issues from the single orifice of a steatite burner, and 

 reaches a height of 24 inches. The slightest tap on a distant 

 anvil reduces its height to 7 inches. When I shake this bunch 

 of keys the flame is violently agitated and emits a loud roar. 

 The dropping of a sixpence into a hand already containing 

 coin knocks the flame down. I cannot walk across the 

 floor without agitating the flame : the creaking of my boots 

 sets it in violent commotion. The crumpling or tearing of a 

 bit of paper, or the rustle of a silk dress, does the same. It 

 is startled by the patter of a raindrop. I hold a watch near the 

 flame : nobody hears its ticks ; but you all see their effect upon 

 the flame : at every tick it falls. The winding up of the watch 

 also produces tumult. The chirrup of a distant sparrow shakes 

 the flame down ; the note of a cricket would do the same. From 

 a distance of 30 yards I have chirruped to this flame, and caused 

 it to fall and roar. I repeat a passage from Spenser : the 



* Numerous modifications of these experiments are possible. Other in- 

 flammable gases than coal-gas may be employed. Mixtures of gases have 

 also been found to yield beautiful and striking results. An infinitesimal 

 amount of mechanical impurity has been found to exert a powerful influence. 



