Evening star., 1911-08-17
SOUND IN THE UNIVERSE.
How the Earth's Atmosphere Act:
as an Effective Muffler.
From the Scientific American,


We live and move at the bottom of an
ocean of air. the earth.s atmosphere. One
consequence or this is that every me-
chanical disturbance starts waves OF com
preston and rarefaction, which radiate
out from the source, and, striking the
drum Of our ear, may df of the right
strength and quality) cause in us the
sensation of sound Among such sem
sations some affect us merely as noises"
in others We recognize a more or less
we'll defined musical pitch and tone
quality" Physically the noise differs
from the musical note in that the for
mer is an irregular disturbance. while
the latter is periodic and of definite fire.
quency. Not that there is any hard and
fast line of demarkation: rapid success
sion of impulses, which separately would
be mere noises, may impress the ear with
a definite sense of pitch. Thus the teeth
of a saw, cutting In rapid sequence
through a wooden board, produce q sound
of definite pitch. though lacking, perhaps,
in musical quality. Or again, a sharp
noise of brief duration, proceeding from
a point in the neighbor hood of a series of
equi-d!stant obstacles, such as a line of
fence rails, or flight of stone steps,
produces upon the observer a EenSation
in which a more or less well defined pitch
can be recognized. The explanation of
this phenomenon Is that the sound is re-
fiected back from each fence rail in turn,
and since it takes time to travel, each
echo reaches the observer a trifie later
than that from the neighboring rail. This
case is of special interest. because the
soand heard contains an element quite
foreign to the initial disturbance. Fur
thermore, the pitch of the sound heard
differs according to the location OF the
observer. so that, borrowing an express
sion from optics, it might be said that
the original disturbance is ''analyzed" by
reflection from the fence tgrating) into
its constituent waves-each travelling
In its own direction. so that it can be
singled out by the observer. 1t is posi-
BILE that the means commonly employed
TO analyze light waves act in this way.
and perhaps we are not quite justified in
imagining white" light, for instance. as
composed" of the various spectral col
ors these being rather impressed upon 1T
by the prism grating or other device
employed to ''analyze" the light. as We
commonly say.
OF all the forms of energy, sound would
probably be of the least consequence to
man. were il not for the one important
fact that sound is the normal vehicle
for the transmission of intelligence be-
tween individuals. Certain special sounds
are recognized by us not merely as
noises" or musical notes." but as
words" which are associated in our
minds with definite concepts. and whose
mere mention Immediately summons up
before our Imagination the concepts thus
attached to them. Not that speech eX-
hausts all the modes of sound-expression
for mental states at our command In
deed, more elemental and lower In the
scale than speech are various inarticulate
sounds, such as laughter and crying. calls
OF various kinds. the groan of pain. the
sigh of relief. the shrek of fear. and
host of other emotional expressions. In
these man approaches more nearly TO the
lower animals, who also possess calls.
But the range of our modes OF expression
by means of sound extends also on the
other the heroic side, beyond ordinary
speech The poet by rhythm and cadence
conyeys something more than his words
alone would say, and in the symphonies
of the great masters of music. there is
borne In upon a wealth of thoughts
that lie too deep for words.