The sun. [volume] (New York [N.Y.]) 1833-1916, 1898-09-18
SOUND BY PHOTOGRAPH.
PROF. WEBSTER'S INVENTION AND
THE WORK 1T DOES.

Converts Sound waves Into waves OF Light
and Then Measures Them Exnotly-Proves
There IL No Such Thing as Actual silence
Work of the sOund-OonvertinR Machine.
= Prof. A. @. Webster Of Clark University has
perfected a scientific instrument which is
likely to add considerably TO existing knowl-
edge of the phenomenon OF sound. At the re-
cent meeting Of the American Association
for the Advancement OF Science Prof. Webster
advanced the question. slow loud is q
soundf" When nc one was able 20 answer he
brought into view an apparatus which served
as an absolute standard OF comparison. Here
after II will be possible to say Just how loud
any sound may be. not by Ruesswork, but by
means OF waves made by reflected light. Inci-
dentally Prof. Webster remarked that with
this instrument Il may be possible to chase
the echo to It's source and find out all about It;
that a modified form OF the instrument might
be installed on shipboard TO be used TO denote
the approach Of other vessels.
Light IL the agency that has been called in to
increase the knowledge OF sound. 1t ls by
means OF photography that Prof. Webster
measures all sorts OF noises, from the roar OF
an explosion to sounds 30 low that the human
ear fnds 1t 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 ac-
ceptance OF the term. What men call silence
includes oil noises below the limit at which
the human ear will register sound. but silence
Is really full OF sounds that pass unnoticed,
except by some delicate perception like that OF
Prof. Websters apparatus. In other words,
silence Is comparative and not positive.
There are probably few sounds that can es-
cape this new invention, for its maker has
proved that with 1t he can detect and photo
Nn0~h NIA III >.ol& L. . -.lA ~
passing through a room.
The mechanism by which Prof. Webster's
machine records sound ready for measure
ment is comparatively simple. 1t consists Of
a set of movable mirrors and prisms which act
In conjunction 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 1t suppose
that light Is admitted through a pIn-hole shut
blade. for example. and observe the shadow
see, that the edges OF the Shadow are TfriSgeedi
with oolored light. The light In passing by the
edge or back Of a razor or Q block OF marble or Q
the same way. This Is because light always Is
Infected. or, moro properly speaking, refract-
Il is rarely observed In ordinary circumstances
because when light comes from various dlrec-
lions tsgnct the &c co EIS%5TitseOOamapg composing Il overlap and are
stance OF excessive thinness reflects brilliant
oolors. Examples are seen In thin lamine OF
iHterstlces between plates Of mica, also In thin
films Of oil on water and alcohol on glass, but
most remarkably in soapy water blown into
The same effect .is produced II a lens Of
plight eonyexity Is laid on q plane lens. and the
viewed by reflected light. Rings Of color may
be- seen ranged around the point Of contact.
liant and each one contains the colors Of the
spectrpm II their order. These are common
Ne S Stiled hr SsT TSH%estiF FiHssSs' t Sssaus Sb Sir 6saao
This principle Of infection, then. and a modif-
cation Of the instrument, used In producing
for measuring sound. Within a small square
box Prof. Webster has placed several mirrors
e eInr5P T Rih Be- i Pro ssse I a %1nPss a t moti MsT Es :
tive Photographic, plate. On one side Of the
boy Is a globe-shaped ,resonator., inside OF
vTbhfp1c n ls a sehsitlVe diaphragm made OF a very
The slightest sound will cause this diaphragm
phragm Is attached a very small circular mir
q sound, howevsr slight. enters the ,resonator
$aekysrd and forward arc and snri a sr1l2f BEAM eaIrae q
mirrors and the prisms and is made finally to
resolve itself into a series Of colored frinRes.
Of Sits in a screen e pnI1iV by the 6er time the + s iigSt
reaches the Photographic plate it takes the
form OF q waving line. This waving line Is pro-
may be viewed If necessary by a number Of
persons at once, as during the meeting Of the
American Association for the. Advancement Of
Science. So, rs Prof. Webster, j~ocularly re-
marked, a deaf maj might easily distinguish
fh 1i difference between the sounds. while a
Some surprising results were shown on the
screen. Thus the vibrations produced by a
tuning fork were shown in the form Of very
regular waves across the screen. Some vowel
sounds. projected into the receiver were de-
Hlcted In Q very irregular waving line. showing
voice evenly. While pronouncing a letter or
word. This is q point for musicians and sing
e,rs generally to ponder over. A draueht In
a series Of rather irregular curves having a
downward trend. Silence manifested itself in
a series OF very regular fine waving lines.
Ability to hear or see silence might occasion
some surprise. but the, record proved simply
that there were sounds in the atmosphere
Thich. the human ear could not hear. Lord
Kayle5Gh, after some eXperimentation. deter
Of an Intensity less than one-millionth Of an
atmosphere. Some idea OF the capabilities of
this new instrument may be gained from the
faGt that the little, mirror mentioned above
slight. a distance. as 1-100.000 OF an inch.
Prof. .Webster's new machine may prove Of
great scientific value. 1t has recorded a sound
tan Sao Of S'1 tWenty feet 81 AZ H "ff% orfSPLdSe feet &c ? t dlst
same sound. then reduced to one-twelve-mil-
lionth, OF ar atmosphere. VAS recorded. On
the other hand the sound Of a whistling buoy
OF this sound and the distance away we're do
termined by the instrument. And this brings
up the question OF Its utility on vessels. II
on On other vessels carving such an apparatus
much lessened if the collision itself we're not
rendered absolutely impossible.