SENSITIVE FLAMES. 
157 
in Plate VIII. Fig. 1 is the tall flame, with its dull, smoky, un- 
steady appearance, and its loose, ill-defined shape. Fig. 2 is 
the same flame under the influence of sonorous vibrations ; it 
has fallen a height of six to nine inches, and widened out some 
three inches ; the half-burnt gas, the clouds of carbon, the lack 
of definition have gone, and all this wondrous change has been 
brought about by the influence of a little noise.* 
Some amusing experiments, dependent on this change in the 
luminosity and shape of the flame, at once suggest themselves. 
One may retire to such a distance from the flame that small 
print shall be illegible, but, by whistling, the flame maybe made 
to diverge, and as long as you whistle you can see to read. Still 
more effective for lecture illustration is the following. When 
the flame is burning upright, any combustible substance, as 
matches, gunpowder, gun-cotton, or a strip of paper, may be 
placed about an inch from the middle of the flame. A stroke 
on the c above the treble of a piano, a whistle, or a clap, 
will at once diverge the flame and ignite the neighbouring sub- 
stances. 
This remarkable change in the aspect of the flame is wrought 
solely by the effect of sonorous vibrations, and is not at all due 
to the impact of the puffs of air which may have attended the 
production of the sound. Nothing material has been translated 
to the flame. The particles of air, if ever so violently displaced, 
could not struggle onward, even for a short distance, through 
the entangled barrier produced by their surrounding neighbours ; 
and, could they reach the flame, their impact would be incompe- 
tent to produce an effect so strange and sure. It is solely the 
wave-like, to-and-fro motion of the air, by which sound is pro- 
pagated from place to place, that has caused this change. It is 
the product of translated motion , not of translated matter . 
But any lingering doubt as to the possibility of some tangible 
connection with the flame will speedily disappear. Let a person 
go whistling out of the room in which is the sensitive flame, 
and let the door and every opening be closed after him. If he 
continue to whistle, the flame will still respond, though with 
enfeebled power as the distance increases and obstacles arise in 
the path of the sonorous waves. Still let your friend go on 
whistling, as he retreats into some upstairs room two or three 
stories away. The flame, if properly sensitive, will be visibly 
affected every time the faint sound of the whistle is heard. The 
velocity with which sound is propagated is here well illustrated, 
the movement of the flame being' simultaneous with the hearing 
of the sound. 
* For the representation of these flames and the other drawings on the 
plate, I am indebted to the skill of my friend Mr. Hedman. 
