National Republican., 1881-04-22
LIGHT AND SOUND.
PROF. BELLS RECENT DISCOVERIES,
As Described Before the Academy of Science-The
Production Of Sound by Radiant Energy
An Interesting Investigation OF
Photophonic Phenomena.

L
elected members. There were two more yaean-
cies and large number of candidates for admis-
sion; but the contest was so stormy that it was
determined not to make any further elections
The following members Of the council were
elected: Professor S. F. Baird, Professor Wolcott
Gibbs, Cambridge; Professor A. Hall, o. S. N. Pro-
fessor J. E. Higard, Coast Survey; Professor Clar-
ence King, Professor Fairman Rogers, Philadel-
phia. Professor Simon Newcomb was elected
home secretary and Professor J. H. c. Coffin, u S.
N, treasurer. The academy then adjourned and
resumed its session at two o'clock.
WELL ATTENDED SESSION.
There was u larger attendance of the members OF
the academy and visitors than at any preceding
meeting The windows were darkened from the out
side, and one gas-jet gave dim light ms
preparation had been made on account OF the
stereoscopic views used in illustration of the
paper upon "The Production of Sound by Radiant
Energy which was read by Professor A. Graham
Bell He is well known as the inventor of the
Bell telephone. He has a striking personal ap-
pearance, being above the medium height, and
of powerful physique. His features. which are
quite dark, are surmounted by heavy growth of
Wavy black hair, and fringed with black whiskers.
His manner betrays what his accent gives US in
dication of-his French origin. He was closely
confined to his manuscript, but at especially in
teresting portions he would speak ex tempore,
with great earnestness of voice and manner. He
illustrated his papers by stereoscopic views, which
were projected upon the wall behind the pres1-
dents chair. He was followed very closely by the
members of the academy, and was frequently ap-
plauded. The following is the
SYNOPSIS OF PROFESSOR BELLS PAPER.
Experiments, he said, had led him to believe
that sonorousneSS would be found to be a general
property of all matter when exposed to the action
of rapidly interrupted beam of sunlight The
first experiment was as follows: A beam of sun
light was focused into one end of an open tube,
the ear being placed at the other end. Upon in
teTupting the beam clear, musical tone was
heard, the pitch of which depended upon the fire.
Quency of the interruption of the light, and the
loudness upon the material comprising the tube.
Later in Paris Professor Bell made an experiment
which permitted him to test the more general
that sonorousneSS under the influence
of intermittent light is a property common TO all
matter. The substance to be tested was placed i'll
the interior of q transparency, which was trans
parent to light but practically opaque to sound.
The preliminary experiments in Paris were so
promising that Mr.. Tainter carried on the investi
cation III America, Professor Bell having written
to him from Paris as follows;
Place the substance to be experimental with in
of the teube placing the other end of the pipe TO the
ear Then focus the Intermittent beam upon the sub
stance in the tube. have tried large number Of
substances in this way with great success although il
IS extremely difficult get glimpse of the sun here,
and when does shine the intensity of the light is not
to be compared with that TO be obtained in Washing
ton. got splendid effects from crystals of bchromate
potash crystals of sulphae of copper and from to-
bacco smoke. whole cigar placed in the test-tube
produced q very loud sound. could not hear any
hing from plain water, but when the water was dis
,olored with ink feeble sound was heard. would
suggest that you might repeat these experiments and
extend the results, &c.
Mr.. TAINTER's EXPERIMENTS.
Mr. Tainter was led by his experiments gradu-
lily to the discovery that cotton wool, worsted,
ILL, and fibrous materials generally produced
much louder sounds than hard, rigid bodies like
.rystals OF diaphragms, such as had hitherto been
Ised. He found that the darkest shades produced
he best effects. Such marked re- enforcement
# the sound resulted from darkening some cot
on wool with lamp black that he was induced
o try lamp-black alone. The sound produced
vas much louder than any heard before. When
he beam was thrown into a resonator, the in
erior of which had been smoked over lamp, most
urious alterations of sound and silence were
deserved. The extremely loud sounds produced
rom lamp black have enabled US to demonstrate
he feasibility of using this substance in
AN ARTICULATING PHoToPHoNE,
n place Of the electrical receiver formerly en-
'loyed. In regard to the sensitive materials that
an be employed, the experiments made indicate
hat in the case of solids the physical condition
nd the color are two conditions that markedly
influence the intensity of the sonorous effects.
he loudest sounds are produced from substances
n loose, porous, spongy condition. and from
hose that have the darkest or most absorbent
olors. Professor Bell explains the sounds pro-
uced from such substances by the heating and
expansion ofthe particles, causing
A CONTRACTION OF THE AIR SPACES,
r pores, among them, by which means he thinks
wave of condensation is started in the atmos-
here. I'VE can thus understand" he says, - how
is that substance like lamp black produces in
ense sonorous vibrations in the surrounding air,
While at the same time it communicates avery fee
lie vibration to the diaphragm, OF solid bed, upon
which it rests" In this connection, however, Pro-
essor Bell disagrees with Mr. Preece, the English
centist holding that i'll the case of thin disks
cal vibration of the diaphragm is caused by the
ction of the intermittent beam, independently of
ny expansion and contraction of the air confined
n the cavity behind the diaphragm" He has not
ct found one solid body that has failed to become
onorous under proper conditions. Similar ex-
eriments with liquids produced the following re-
ults:
lear water ... .... No sound audible |
Water discoiored by Feeble sound
iereury sound heard
uiphurlc ether
AmmOIlia a.............--..
.mmonia- -suphate Of copper...-.. Feeble, but dis
Writing tnct sound
indigo in suiphuIic acid......-....--
'hIorlde OF copper ........-.....-.-.....J
sulphuric ether and chloride of copper gave the
est sounds. An experiment was made, at the |
1ggesticn of Professor Tyndall by filling one test
Ibe with the YapoT of sulphuric ether Ia good |
bsorbcnt of heat and another with Yapor of BIZ
1lphide of carbon "a poor absorbent), and it was |
ound that the sound was louder in the former |
ase than in the latter. The vapors of the follow
ne substances were found 70 be highly sonorous |
n the Intermittent beam: Water vapor, coal gas, |
ulphuric ether, alcohol, ammonia. amylcne ethyl |
rOmide, diethylamene mercury, iodine, and per- !
xide of nitrogen. The loudest sounds were OBJ |
lined from iodine and peroxide of nitrogen.
An IMPORTANT DISCOVERY.
As result of these experiments it has been found
nat lamp-black could be employed in place of
elenium in an electrical receiver, and the impor-
snce of the discovery is very great, especially
Ihen Se consider the expense of such rare sub
ances as selenium and tellurium. We have also
1und that loud sounds are produced from lamp
lack by passing through it an intermittent elec-
-ical current, and that it can be used as a tele-
homie receiver for the reproduction of articulate
peCch by electrical means.
The paper gave description and noted the re-
llts Of some interesting experiments made for the
urpose of measuring the sonorous effects pro-
uced by different substances.
THE SPECTRUM.
It also showed the curious results of passin" an
ltermittent beam from an electric lamp througha
riSon and then examing the audible effects pro-
uced in different parts of the spectrum. A con-
nuous increase i'll the loudness of the sound was
bserved upon moving the receiver gradually from
le violet into the ultra-Ted. The point of maxi
lum sound lay very far out in the ultra-red. Be-
ond this point the sound began to decrease, and
len stopped so suddenly that very slight mo-
OF OF the receiver made all the difference be-