338 On the Recognition of Noises. [June, 
report of fire-arms, but more feeble and selected for this 
purpose lead pipes from which a stopper was driven by com- 
pressed air with a strong puff. This produced a series of 
projections of decreasing strength. But if the tubes were 
filled with loose cotton-wool so that the fluctuation of the 
air was checked, the stopper flew out almost without noise. 
If secondary fluctuations of the air occur in the lead tubes 
they must happen also on discharging a rifle or a cannon, 
and we can no longer deduce the deep tone in the report of 
the latter exclusively from the dimensions of the primary 
wave. We hear in the report of fire-arms a very brief sound, 
a sound too short to be recognised as such, and whose 
primary impulse, when sufficiently near, simultaneously 
excites all the cochlear fibres. 
In a child’s rattle, the noise of which is the higher the 
more the tongue is shortened, in the blows of a hammer, in 
stamping, &c., the noises must be judged in the same 
manner. The character is determined by the secondary 
vibrations of the parts which come in contact, and of those 
which are in such connection that they are simultaneously 
set in vibration. If they last long enough we have the pro- 
duction of a sound; if they are too short we have a noise 
the character of which depends on the period of the secondary 
vibrations. 
If we examine experimentally what influence the length 
of a sound-wave exerts upon the auditory sensation which 
it produces, soap-bubbles filled with detonating gas are the 
most suitable. They must not exceed a certain size, other- 
wise all the fibres of the auditory nerves are in all pro- 
bability affeCted together. The experiments showed that 
with a suitable mixture of air and hydrogen the large bubbles 
gave a duller, therefore a deeper, sound than the smaller 
ones, though the explosions showed only a single projection, 
and consisted therefore only of a single wave. The acoustic 
difference appears therefore with a single wave just as in the 
explosive noises which, besides the primary wave, produce 
also secondary vibrations. In both cases the character of 
the sound is determined by the especial excitement of a part 
of our auditory nerve fibres. 
It is known that no deep tone can be produced by the 
movement of masses of air caused by single high explosive 
noises, even if the separate impulses of the air follow 
slowly upon each other. On this subject we can refer to 
former experiments with Savart’s wheel. The reason must 
be that each single one of these noises does not set the 
lower tissues of the internal ear in such a vibration that its 
