38 CHELTENHAM COLLEGE NATURAL HISTORY SOCIETY. 
SINGING FLAMES. 
Rr. Davis said the phenomena which he was about to 
>} bring under their consideration were for the most 
part instances of vibrations, maintained by heat, 
| which gave rise to continuous sounds, 
Before proceeding to the phenomena themselves, he would, as 
shortly as possible, state a few elementary principles of acoustics 
on which they depended, in the hope that by so doing the explana- 
tions he should give would be readily understood by those present 
who might happen to have little previous knowledge of the subject. 
The air was a very elastic substance, and like other elastic sub- 
stances was readily put into a state of vibration, and, the effect of 
these vibrations on the ear was to produce the sensation of sound. 
When a disturbance was caused at any point in an elastic medium 
the disturbance spread outwards, giving rise to a wave. Now, there 
were two kinds of elasticity, and those two kinds of elasticity gave 
rise to different kinds of waves. There was the elasticity which 
arose from the tendency a substance had when put out of shape to 
recover its original form. Such was the elasticity of a steel spring, 
a piece of indiarubber or a mass of jelly. Air had no elasticity of 
this kind. The other kind of elasticity was that which arose from 
the tendency a substance had when squeezed together or opened 
out to recover its original volume. This kind of elasticity air pos- 
sessed in an eminent degree, and it gave rise to waves of compres- 
sion and rarefaction. 
The difference between the two kinds of waves, corresponding 
to the two kinds of elasticity, was illustrated by a model consisting 
of a strip of wood from which were hung a row of bullets, each bul- 
let being hung from a thread about a foot long. By pushing the 
bullets aside by a board, tilting the board so that it was higher at 
one end than at the other, and then lowering it, the bullets were 
released one after the other, and the swing given them was such as 
to cause a succession of waves to run along the line of bullets. The 
kind of waves so produced corresponded to distribution waves, or 
waves arising from the force with which a substance resists a change 
