The Press.
London, England, 1854-07-22 00:00:00

JULY 22, 1854.

enveloped in Lady Rycot's cashmere shawl the little fellow
on whom he had just conferred twenty thousand a year and
a peerage, he called in a peremptory tone to the girl who
was assisting Dame Stubton, to "come down, and take
care of ' the child.' "
All he trusted was that its little fitful life might not hold
out till Luke Harston's return.
The rain had luckily ceased. And as the doctor splashed
his way along the puddley by-road leading to the village, so
far from feeling conscious-stricken at the felonious act ho
was perpetrating, his sensations, while hugging the little
changeling under his warm surtout, were those of a bene-
factor. He was securing wealth and distinction to the
child of poor Bessy ; and her spirit, hovering like a guar-
dian angel above them, could not fail to prosper his design.
By the time he had established his little nursling under
the wing of the ignominious nurse who was to afford him
the sustenance so much more needful to the convulsed and
*agile offspring of the aristocracy, whose hours, nay, whose
minutes, were numbered, he began to look upon the new
Lord Hilton as almost a creation of his own.
The last half of the volume is not so well
written as the earlier portion, which raised
our expectations. In spite of the defects of
construction, " Transmutation," while failing
as a novel, may be pronounced readable as a
romantic " tale."

Sound and its Phenomena. By the Rev. Dr.
Brewer, Trinity Hall, Cambridge. London :
Longmans.
THIS volume is the first of a series of scientific
handbooks, which the author proposes to
issue chiefly for the use of schools, industrial
families, and classes. The nature, transmis-
sion, and velocity of sound are first described,
and then the author treats of various kinds of
musical instruments, of the voice, with the
apparatus of the larynx, and lastly of the ear,
with all that exquisite mechanism which ren-
ders it one of the most interesting parts of
the human frame.
Dr. Brewer is successful in showing that all
sound is originated by motion, and that it con-
sists in certain vibrations of the air, which he
terms " wave-sounds," buthe appears to imagine
that sound is something positive in itself, and
does not wholly depend on the construction of
the ear. On this point there exists some
difference of opinion among those who have
studied the subject most closely; and philoso-
phers have generally shrunk from the conclu-
sion that sound is nothing more than that
impression which is made on the tympanum
of the ear by certain vibrations of the external
air, which it is expressly formed to receive and
to transmit.
If such be the correct theory, then, apart
from the original impulse given to the air (or
other elastic body), there is required, to excite
that perception which we call sound, a me
dium to convey the original impulse and an
ear formed to receive it ; and, if either be
wanting, the conditions essential to produce
sound are absent. Now, many instances and
experiments can be adduced to show that
there is no sound without these conditions.
Just as certain properties of matter excite the
nerves of the nose and produce the sense of
smell do vibrations of the air act on the ear
and produce the sense of sound. Our organs
of sense are all acted on by external influences ;
and, strictly speaking, perhaps, the five senses
may be reduced to one, that of feeling, as the
eye, ear, nose, and tongue act only by directly
feeling or perceiving the influences which ex-
cite them.
Throughout his book Dr. Brewer uses the
term sound as synonymous with that vibra-
tion of the air which results in sound when
the ear is acted on; and, so far, his language,
though sanctioned by custom, is, we think,
unphilosophical :
Sonnd-waves (he writes) are engendered in the air by
whatever gives it a sudden shock : as by the rapid impulses
of some vibrating body; by a solid substance rapidly and
suddenly changing its place; by the percussion of one
stratum of air against another ; or by a combination of
some two or more of these collisions. • • •
The sound-waves thus created diffuse themselves in
concentric circles around the point of their birth, not
unlike the ripples made by a stone when it falls into
tranquil water.
--waves would here, as in all other places
igh the book, be a more correct expres-
than sound-waves, if it be admitted that
can be no sound apart from the ear.
Brewer then goes on to show how the
IeSS of sounds is proportionate to the
of the shock- which the air receives :

THE PRESS.

The analogous ripple on the smooth surface of a lake
would be tkr more deeply furrowed by the violent shock of
a millstone than if a small pebble were dropped gently

into the water.

And as the ripple diminishes in force u it
recedes, until it is altogether imperceptible,
air-waves diminish as they recede from their
source until they wholly die away. Ripples in
the air, however, are weakened sooner than in
water, as they are diffused in all directions,
" like the light of a lamp, or a candle ;" and, in
accordance with this principle, it is found that
sound diminishes in intensity with the squares
of its distance from an auditor. Thus :
Conceive four men placed at equal distances from each
1 2 3 4 other, as the let-
) I t r I ters B, C, 1), E,
n 0 n s along the line
AE. Let some one tire a pistol at A ; then to C, who is
twice a 9 far off as B, the sound will be only one-fourth as
loud ; to I), who is thrice as far off, it will be but one-
ninth as loud; and to E, who is four times the distance,
it will be only one-sixteenth.
On the other hand, with whatever degree of intensity E
may hear the sound, D will hear Rime times as loud, C nine
times, and B sixteen times a 9 loud as E. So that the loud-
ness does not diminish inversely as the distance increases,
but inversely to the square of that distance.
We do not recollect whether experiment has
ever shown that a ripple in the water extends
or travels at au uniform rate of speed from its
centre ; but this is certainly the case with air
or sound-waves.. They progress, whatever
their character and degree of intensity, at an
equal rate of velocity. That rate in the air is
taken for all practical purposes at 1,120 feet in
a second, and is found to be in no degree
affected by distance from its source. When
the air is rarer than common, through heat,
sound travels faster than when it is denser
than common through cold, the air in the
latter ease offering more resistance than in the
former to the transmission of the original im-
pulse it receives. On the other hand, the
denser air is found to convey sound more per-
fectly :
As cold condenses the air, sounds are heard more dis-
tinctly daring a clear frosty day than in the hot noons of
summer.
For the same reason, they are more audible in the frozen
regions than in climates of a higher temperature.
Captain Ross tells us, that when he was wintering in the
polar seas he could hear the voices of his men in conver-
sation at the distance of a mile and a half. And Lieutenant
Foster on one occasion, during the third polar expedition
of Sir Edward Parry, held a conversation with a man on the
opposite shore of Port Bowen, the distance between the
speakers being smile and a quarter.
We have heard Mr. Kennedy (who com-
manded the Prince Albert in the search for Sir
John Franklin) relate that, having once, when
alone, lost his way amid the trackless snow,
he shouted for help and was answered at a
great distance. He followed the sound, and
at last came to some Esquimaux. On subse-
quently comparing the points at which they
stood when they first heard each other, he
found that they must have been seven or eight
miles apart—so far in the dense atmosphere
were the air-waves propagated which their
voices excited.
Though, as we have seen, rare air conveys
sound most quickly, yet denser media are
stated to propagate sound with far greater
velocity than air :
Sound propagates itself in water more than four times as
fast as it spreads through atmospheric air. * • • •
Solid substances for the most part convey sound still
more rapidly than water, and in some cases with a velocity
14' or DI fold greater than its rate of motion in atmospheric
air. • • • • • ••
The rate at which sound is propagated by various solid
substances has been carefully tested by Chladin. • • *
Glass, iron, and steel transmit sound the fastest. Next,
willow, pine, and common deal. Of metals, tin transmits
sound the most slowly ; and of woods, oak, walnut, yew,
and plam.
If these facts are to be taken as literally
true, they offer considerable difficulty to the
theory, that sound is caused by vibrations per-
ceived by the ear alone. In the case of water,
we am understand that vibrations or pulsa-
tions made in that fluid may act on the ear in
much the same manner as vibrations of air;
but it is not so easy to perceive how the ear
can be affected through the medium of solid
substances, more especially if those substances
are not in direct contact with it. Some
medium between the original impulse or sound
and the ear there must necessarily he, and
that medium must plainly be the air in all
those cases in which sound is said to be con
veyed by solid substances ; but whether the

689

solid body conveys the original impulse from
one of its extremities to the other, and then
imparts the impulse to the air, or whether
the air at the surface of such solid body
transmits the impulse much more quickly
from the slight resistance of the surrounding
atmosphere, deserves inquiry. The following
experiments are curious :
If. Biot has satisfactorily tested the relative velocities of
sound as conducted by air and by metal. A bell was
suspended at the mouth of an iron pipe 3,000 feet in length,
and a metal ring was so adjusted round the orifice that, when
the bell sounded and transmitted its vibrations to the air
contained in the tube, the ring struck against the conduit,
and communicated vibrations to its metal walls. In this
experiment, the vibrations of the ring conveyed along the
sides of the tube reached the ear of the observer a con•
siderable time before he heard the sound of the bell.
The following would be interesting variations of the
same experiment, and capable of easy trial. Let
some one fire a pistol at one extremity of a long gas-pipe,
and the person who applies his ear to the other end will
hear the report twice. He will hear it almost instanta-
neously, as it is conducted along the metal walls of the con-
duit, and again, a considerable time afterwards, as it comes
lagging through the ambient air.
Or, again : if at early morning, when the air is calm and
the neighbourhood quiet, you apply your ear to one end of
the handrail of an iron bridge, while some one at the other
extremity strikes upon the bar or parapet, you will hear
the report of the blow tweet. The first and loudest will be
delivered by the metal, and the second by the air.
N.B. Sound traverses iron somewhat more than sixteen
times hater than it circulates in air.
On these facts the reasoning of Dr. Brewer
seems to us partly true and partly false :

The last two experiments (he writes) could not of them-
selves be admitted as proof, though they may be taken as
corroborative evidence of the point under consideration.
It will be seen that the circumstances are not equal,
inasmuch as the sound-waves have, in one case, the whole
field of air, in which to spread in constantly enlarging con-
centric circles. whereas in the latter they can propagate
themselves only in one direction. In the former case the
diffusion is by squares, in the latter by lines. This objection,
however, does not rest against the experiment of M. Biot,
inasmuch as the air was confined in a tube. And as the
result in all three cases is exactly the same, the objection
is in reality of no valid force.
It appears probable that in the experiment
of M. Biot the air in immediate contact with
the surface of the pipe might convey the
vibrations of the bell more quickly than tho
air contained in the hollow of the pipe ; but
we do not venture further than to suggest the
expediency of more inquiry, with original
experiments, on this very interesting subject.
If from such a pipe the air was exhausted,
and a bell was then rung against its interior
side, the experiment would, we imagine, show
whether the vibration was really conveyed by
the metal or by the air in contact with it.
That solid substances are not of themselves,
apart from the air in contact with them,
adapted to the transmission of those impulses
which produce sound, appears from the fact
that sound is not conveyed through them when
they are of any considerable thickness. A
stone wall, a thousand feet in length, would
convey a whisper along the whole extent of its
surface, but. a much louder sound would not
be conveyed through a stone wall of a single
foot in thickness,—a strong presumption that
it is really the air in contact with solid sub-
stances which conveys the impulse resulting
in sound, and not the solid substances them-
selves.
That sound does not exist apart from some
media for its conveyance, and apart from the
ear communicating with such media, is proved
by numberless and familiar examples. If a
bell be rung in the exhausted receiver of an
air-pump, no sound is apparent ; admit the
air by degrees, and by degrees the sound is
heard. Place over the receiver a larger re-
ceiver, and exhaust the air from the second
while it is retained under the first, and the
ring of the bell will again not he heard, be-
cause the communication of air between the
bell and the ear is cut off. Supposing a per-
son were placed under the first receiver, be
would hear the ring plainly enough, while to
a person outside of the second receiver the
clapper would seem to strike the bell without
causing any sound whatever. The conclusion
seems to be, that sound consists alone in the
adaptation of the ear to receive, and to per-
ceive, vibrations of the air.
Some paragraphs here on the effects per-
ceptible by persons who have ascended to a
highly-rarefied atmosphere point to the same
conclusion :

Air-,
throuo
Sion ti
there
Dr. B
loudno
force 4