The Cook County herald. [volume] (Grand Marais, Minn.) 1893-1909, 1899-02-04
HOW TO SEE SOUND.
SLIGHTEST NOISE is REVEALED
TO THE EYE.
Makes Waves Of .LiEht-Projected to q
Screen and Shown In Highly MaEni-
fed Form-Is Similar to Photography
Says Prof. Webster. ...... =:

of sound. At the recent
meeting of the American Association
for the, Advancement of Science Pro-
fessor Webster advanced the question,
How loud is a sound?" When nc 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
Webster's machine records sound
ready for measurement is comparative
ly simple. It 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
is admitted through a pin hole shutter
into a 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 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 III
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 broadest
and most brilliant, and each one con-
tains the colors of the spectrum il
their order. These are commonly call
ed Newton's rings, because Sir Isaac
Newton first Investigated their phe.
nomena. This principle of infection
then, and 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 a manner that Newton's rings
will be projected against moving sen
sitive Photographic plate. On one side
of the box is a globe-shaped resonator.
inside of which is a sensitive dia-
phragm to vibrate. On the inner side
of the diaphragm is attached a small
circular mirror weighing a fraction of
a gram. When a sound, however
slight, 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 prisms, and is made finally to re-
solve itself into a series of colored
fringes. These fringes are projected
through series of slits 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
a lantern, and may be viewed, if nec-
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
'" "OOoIOA JoSu4dA1 ~ ISmdIh0Q, a. deaf
man easily might distinguish the diff
ference between the sounds, while a.
blind man could not.
Some really startling results we're
shown on the screen. Thus the vibra-
tions 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
point for singers and musicians gen
orally to ponder over. A draft in the
room produced an effect which result
ed in a series of rather irregular curves
having downward trend. Silence
manifested itself in series Of regular,