The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1898-09-18

Prof A. G.. Webster of Clark univer-
sity has just perfected a scientific in
strument which is likely to add consid-
erabiy to existing knowledge of the
phenomenon 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 no one was
able to answer, he brought into view
an apparatus which served as an abso-
lutte standard of comparison. Here
/ after 1t 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, Prof.
Webster remarked that with this in
strument it may be possible to chase
the echo to its source and find out all
about it; that a modified form of the
instrument might be installed on ship
board to be used to denote the ap-
! proach of other vessels.
Curiously enough, light is the agency
that has been called in to Increase our
knowledge of sound. 1t is by means
of photography that Prof. Webster
measures all sorts of noises, from the
roar of an explosion to sounds so low
that the human ear finds it 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 accept
ance of the term. What men call 81
lence includes all noises below the
limit at which the human ear will reg
lister sound, but silence is really full of
sounds that pass unnoticed except by
some delicate perception like that of
Prof. Webster'S apparatus. In other
words, silence is comparative and not
positive. There are probably few
sounds that can escape this new in
vention, for its maker has proved that
with it 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.
1t consists of a set of movable mirrors
and prisms, which act in conjunction
with a diaphram. One of the princi-
pies involved in this part of the proc
ess is hundreds of years old and was
discovered by Sir Isaac Newton. To
illustrate 1T, suppose that light is adj
mitted through a pin-hole shutter into
very 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 a 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 razor or a 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 wilderness. Any transparent
substance of excessive thinness reflects
brilliant colors. Examples are seen in
thin laminae or 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 very thin bubbles.
The same effect IS produced if lens
of slight convexity is laid on a plane
lens. and the two, after being placed
together by a screw are viewed by
reflected 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 color of the spectrum in their
order These are commonly called