The Anaconda standard. [volume] (Anaconda, Mont.) 1889-1970, 1898-10-03
SOUND BY PHOTOGRAPH
Professor Wsbstsr's Invention
and the Work It Does.
FEW SOUNDS CAN ESCAPE
Converts Sound Wave Into Waves OF
Light and Then Measures Them Ex-
actly-Proves There IL No Such
Thing as Actual Silence.

Prof. A. c.. Webster of Clark uni
versity has perfected a scientific in
strument which is likely to add consid-
erably to existing knowledge of the
phenomena of sound. At the recent
meeting OF the American Association
for the Advancement of Science. Prof.
Webster advanced the question. How
loud is a sound?' when nc N was
able to answer he brought into view an
apparatus which served as an abso-
lutte standard of comparison. Here
after IL will be possible to say Just
how loud any sound may be. not by
guesswork. but by means of waves
made by reflected light. Incidentally
Prof. Webster remarked that with this
instrument IL may be possible to chase
the echo to it's source and find out all
about IL: tina a modified form OF the
instrument might be installed on ship
board to be used to denote the approach
of other vessels.
Light is the agency that has been
called in to increase the knowledge OF
sound. IL is by means of photography
that Prof. Webster measures all sorts
of noises, from the roa OF an explo-
sion to sounds so low that the human
ear finds IL impossible to detect them,
and which therefore pass under the
name of silence. The device has proved
that there Is no such thing as silence
in the ordinary acceptance OF the term.
What men call silence includes all
noises below the limit at which the
human ear will register sound. but ST.
lence Is really full of sounds that pass
unnoticed, except by some delicate
perception like hat Of Prof. Webster's
apparatus. In other words. silence Is
comparative n not positive. There
-. -..I.kr, TA.., -A,. sAA -. -
cape this new invention. for its maker
has proved that with IL he can detect
and photograph the noise made by a
draught OF air passing through a room.
The mechanism by which Prof. Web
ster's machine records sound ready for
measurement Is comparatively simple.
II consists of a set of movabl mir
rors and prisms which act in conjunc-
ton with a diaphragm. One of the
principles involved in this part of the
process is hundreds of years old and
was discovered by Sir Isaac Newton.
To Illustrate II suppose that light was
admitted through a pin-hole shutter
into a very dark room. Introduce into
the panel of hight any opaque body. as
a knife blade. for example, and observe
the shadow which IL casts on a white
screen. and we shall see that the edges
of the shadow are fringed with colored
light. The light in passing by the edge
or back of n razor or a block OF marble
or a bubble of air in glass is in each
case affected the same way. This is
because light is always infected. or.
more properly speaking. refracted,
when IL passes by the edges of bodies.
But ii is rarely observed in ordinary
circumstances eau when light
comes from various directions the coll
ors composing IL overlap and are re-
duced to whiteness. Any transparent
.,,As,ap.a 90 a~,agsi.a fhf,naaa ,aef.,4.
brilliant colors. Examples are seen in
thin laminae OF air occupying cracks in
glass and the interstices between plates
of mica. also in thin films of oil on wa
ter n alcohol on glass. but most re-
markedly in soapy water blown into
very thin bubbles.
The same effect is produced IL a lens
OF slight convexity is laid on a plane
lens. and the two after being placed to-
gether by a screw are viewed by re-
fiected 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-
tains the colors of the spectrum in their
order. These are commonly called
Newton's rings. because Sir Isaac New
ton first Investigated their phenomena.
This principle OF infection, then, Inc a
modification of the instrument used in
producing Newton's rings are used i'm
the new apparatus for measuring
sound. Within a small square box
Professor Webster has placed severai
mirrors and prisms In such a manner
that Newton's rings will be projected
against a moving sensitive Photographic
plate. on one side of the box IL a globe
shaped resonator. inside OF which is a
sensitive diaphragm made Of a very
thin glass plate.
The slightest sound will cause this
diaphragm to vibrate. On the inner side
OF the diaphragm is attached a very
small circular mirror weighing a frac-
ton of a gramme. When a sound, how
ever slight. enters the resonator or re-
ceiver OF tho instrument the diaphragm
and consequently the small mirror vi
brate backward and forward and a
small beam of light is sent careening
about among the other mirrors and the
prisms and is made finally TO resolve IT.
self into a series OF colored fringes.
These frlnges are projected through a
series OF Sits i'm a screen until by the
time the light reaches the Photographic
plate IL takes the form of a waving line.
This waving line is projected on a screen
by means OF n lantern and may be
viewed IL necessary by a number of
persons at once, as during the meeting
vancement of science. SO. as Professor
Webster jocularly remarked. a deai
man might easily distinguish the differ
man could not.
Some surprising results were shown
on the screen. thus the vibrations pro-