Year: 1871

NJ PRoF EssOR TYNDALL


Last week, Professor Tyndall deliver
ed the first of series Of lectures on
sound, to large auditory at the Royal
Institution.


DR.. Tyndall began by saying that
sound makes itself known to humen
consciousness by means efobjective and
subjective phenomena. The objective
phenomena exists entirely outside OF
ourselves, and are entirely Independent
of US 40 sound, objectively considered.
Is not sensation at all it Il but a kind
Of motion given to the air. That motor
reaches the brain by some process not
yet unveiled, and perhaps 1t will never
be given to man to unveii how the mo.
tien produces sensation. A very little
observation will show that sound con-
sists of some kind Of mechanical mo
tion. For instance when gun Is fired.
say at Shoeburyness. the observers near
the gun feel shock which disturbs
them from head to foot, ard sometimes
the shock is so great that it will ffutter
an umbrella. Every body also knows
that glass windows may be broken by
loud noises. Sound also is evidently q
kind of wave motion, and not something
projected from the sounding body ; for
instance when a gun Is fir-d, and a / er"
son is placed near it SO as to be perfectly
protected from all projected portions
should it burst, he will hear the noise.


All the foregoing facts about sound
might be learnt in very early times, but
before the knowledge Of the nature of
sound could progress to any great extent,
1t was necessary that other sciences
should grow aud give their aid, the air.
pump and other things had to be inven.
ted before the philosophical mind could
trace its way from tacts to causes. By
means Of the air pump it can be proved
that it Is the air that conveys waves Of
sound.


The speaker then set a small bell
driven by clock work, in motion in a
very perfect vacuum under the receiver
Of an air pump, but not sound was
heard. The objection might be made,
he said, that the glass sides of the re.
ceiver cut off the sound, but he would
prove this not to be the case by letting
the air in gradually. He did SO and as
the air entered, the tinkling OF
the bell made itself perceptible, grew
louder, and finally was clearly heard all
over the theatre OF the Royal Institu-
ton.


The foregoing experiment, said DIR.
Tyndall, might lead to the impression
that the loudness Of the sound depends
upon the densit Of the atmosphere.
He then proved this to be not necessa'
rily the case by very remarkable ex-
pertinent. He admitted air into the
exhausted receiver, till pressure OF
only in. of mercury was exerted inside,
and in this partial vacuum he sat the
bel! to work. A faint tinkle could be
heard. He then let hydrogen gas into
the receiver, 50 as greatly to increase
the pressure aud density of the atnlos'
phere inside, yet Instead Of the sound
growing louder, it gradually became
fainter. Thus increasing the density "i
the atmosphere diminished the sound


He then explained that air has to be
struck violently aud sharply to pro'iuce
a sound. Waving the hand in the air
for instance, does not set up soune
waves, because the disturbed air ha:
time to flow round to the other eide o
the hand, instead of being set in tha
kind Of wave motion which produces
sound. Hydrogen gas he believed to
have the power Of flowing round vi
brating tongue more rapidly than air,
so that it is less easily beaten into sount
waves and this surlnise, which wa.
first mooted by Professor Stokes, he be
lieved explained the true theory Of th'
experiment just shown.


In some other experiments he took
some long polished wooden rods, All,
rubbed them with resiued flannel
whereby each rod in turn was made t
give musical note. In this way h'
proved that deal conveyed sound NOR
rapidly than oak, although oak is tn
denser wood Of the two, 50 it is an erro
to ascribe this power to density.


Professor Tyndall then calle'
attention to the top Of thin woode'
rod projecting 2ft. into the air througl
the floor of the theatre. He said tn
rod went down through two floors of tn
building, and rested at its lower end up
on u musical box. That box was thel
playing, and throwing the rod int
musical vibratory motion, which musi
however, could not be heard In the the
atre because the top Of the rod presenter
too small a surface to the air to set "
good loud sound waves. He then pla
ced guitar on the top of the rod to &C
as a sounding board, aud instantly th
playing of the music box coald be hear
distinctly by erybody. A piece
board instead of the guitar, answered
the same purpose when it was placed o1
top Of the rod. Next, one Of his assis
tants played fiddle, which was place
in contact with the lower end of the rod
and every time the lecturer placed


board on the top of the rod the musi
could be heard.


The lecturer next explained ths
sound travels more rapidly throug


warm than cold air, and whenever til
elasticity Of the air is augmented, III


velocity of sound is also augmented. A


the temperature of % G. the velocity {
sound il 1.090ft. per second, and it au.


ments about eft. for every degre
| nxl.loA IN, Thn uai1A.it