The Princeton union. [volume] (Princeton, Minn.) 1876-1976, 1898-10-20
HOW TO SEE SOUND.
SLIGHTEST NOISE is REVEALED
TO THE EYE.
Makes Waves Of Light-Projected to .
screen and Shown In Highly Magni-
ned Form-Is Similar to Photography
Says Prof. Webster.

Prot. A. g. Webster Of Clark Uni
versity has just perfected a scientific
instrument which is likely to add con-
slderably to existing knowledge of the
phenomenon of sound At the recent
meeting OF the American Association
Tor the Advancement Of Science Pro-
lessor Webster advanced the question,
How loud is a sound?'' When NO one
was able to answer he brought into
view an apparatus which served as an
absolute standard Of comparison.
Hereafter it will be possible to say
just how loud any sound may be. not
by guess work, but by means of waves
made by reflected light Incidentally,
professor Webster remarked that with
this instrument it may be possible to
chase the echo to the source and find
out all about it; that modified form
OF the instrument might be installed
on shipboard to be used to denote the
approach of other vessels.
/ The mechanism by which Professor
FWebster's machine records sound
ready for measurement is comparative
ly simple. 1t consists of set of NOV
able mirrors and prisms which act in
conjunction with diaphragm. One of
the principles involved in this part of
the process is hundreds of years old,
and was discovered by Sir Isaac New
ton. To illustrate it suppose that light
us admitted through pin hole shutter
into dark room. Introduce into the
panel of light any opaque body, as a
knife blade for example, and observe
the shadow which it casts on white
screen, we shall see that the edges of
the shadow are fringed with colored
light. The light in passing by the edge
or back of a razor, or block of marble,
or a bubble of air in glass is in each
case affected the same way This is
because light always is infected, or,
more popularity speaking, refracted,
when it passes by the edges of bodies
But it is rarely observed in ordinary
circumstances, because when light
comes from various directions the col
!ors composing it overlap and are re-
!duced to- whiteness. Any transparent
substance of excessive thinness reflects
brilliant colOrs. Examples are seen in
thin laminas of air occupying cracks
in glass and ice, and the interstices be-
tween plates Of mica, also in thin films
OF oil on water and alcohol on glass,
but most remarkably in soapy water
blown into thin bubbles.
The same effect is produced if a lens
of slight convexity is laid on a plane
lens, and the two, after being placed
together by a screw, are viewed by re-
,fected light Rings of color may be
seen ranged around the point of con-
tact. The smallest rings are broadcast
and most brilliant, and each one con-
ttains the colors- of the spectrum in
their order. These are commonly call
ed Newton's rings, because Sir Isaac
Newton first Investigated their phe-
ynomena. This principle of infection
then. and a modification of the instru-
|ment used in producing Newton's
rings, are used in the new apparatus
for measuring sound. Within a small
square box Professor Webster has
placed several mirrors and prisms in
such manner that Newton's rings
will be projected against moving SEN
,sitive Photographic plate. On one side
tof the box is a globe-shaped resonator,
inside of which is sensitive dia-
phragm to vibrate On the inner side
iof the diaphragm is attached a. small
icircular mirror weighing a fraction of
ia gram. When sound, however
islight, enters the resonator or receiver
of the instrument, the diaphragm. and
consequently the small mirror vi
brates backward and forward, and a.
small beam of light is sent careening
about among the other mirrors and
the prlsms, and is made finally to re-
solve itself into series of colored
fringes. These fringes are projected
through series Of Sits in a screen
until by the time the light reaches the
Photographic plate it takes the form
of a waving line. This waving line
is projected on a screen by means of
lantern, and may be viewed, if nee
essary, by a number of persons at
once, as during the meeting of the
American Association for the Advance
ment of Science. So. as Professor
Webster jocularly remarked, a. deaf
man easily might distinguish the diff
ference between the sounds, while a
blind man could not.
Some really startling results were
shown on the screen. Thus the yibra-
lions produced by tuning fork were
shown in the form of regular waves
across the screen. Some vowel sounds
projected into the receiver were de-
picted in an irregular, waving line.
showing that it is impossible for any
person to hold the voice evenly while
pronouncing letter or word. This is
a point for singers and musicians gen
erally to ponder over. A draft in the
room produced an effect which result
ed in series Of rather irregular curves
having a downward trend. Silence
manifested itself in a series of regular.
fine waving lines. Ability to hear or
see silence might occasion some sur
prise, but the record proved simply
that there were sounds in the atmos-
phere which the human ear could not
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