, 1880-12-19
THE PHOTOPHONE.
Description of tho Latest Scientific
marvel-A Beain Of Light Carrying
Sound.

L 1uE hU1au Nflt4tu1 AICP P<ANS "AbAA e.A@ o~@~A
tiflc surprises of this age. Before sufficient
time has elapsed to mike one startling lnycr-
ton familiar, another equally astonishing is
already the subject Of lectures and newspa-
per articles. Before the telephone, the
1nicrophone, and the photograph have found
their wny into common use, still more ex-
traordinary instrument is announcetl,-o
of which the results are as unexpected by the
scientific as they are Incredible to the ordl-
nary mind. We hear Ut conversation being
carried on by means of trembling beam Of
light, and incrcdulity reaches its climax
when 1t is whispered that the photopllone
may enable us to hear the rise and fall Of
those gigantic. storms that are constantly
sweeping over the suns surface. Is 1t possi-
bic that the revolutions Of modern science
condemned as materialistic and prosalc-can
thus outstrip the widest flights Of the imaeF
nation?
The photophone is the latest development
of Prof Graham Bells ingenuity, aud for Its
scientific novelty, if not for its practical
utility, well deserves {: brief description. One
OF the elementary bodies, named sefeniunl,
and allied to sulphur, is known to undergo
certain changes in its molecular structure
when light fails upon it. These changes
cause the very higll resistance it offers to the
pN5S1kte u dAu ElEElllE CullEIL ~ Wi
and tllis curious effect, hitherto believed to
he unique, has lately been the subject of ill-
vestigatiun by various Englisl! physicists. 1t
occurred to several that this substance might
be employed rs asort Of telephone, q beam
Of light being used to replace the conducting
wires OF the usual forms Of these instru--
ments. Prof. Graham Bell, the discoverer Of
the telephone, to WHOM, amongst Others, this
idea occurred, has had the good-fortune to
throw that thought INTO practical shape:
by means Of tho voice. These vibrations toss
the beam of light slightly to and fro, and
this vibrating beam falls upon selenluln re-
ceiycr, through which All electric current Is
passing, thereby creating slight variations In
the resistances tile current encounters. These
tiny variations III electric resistance can be
detected and rendered audible by that Won
derfuliy sensitive little instrument, the Bell
telephone. This was the conception which
led Prof Bell to announce in Il lecture de-
livered before the Royal Institution SO long
ago AS 1878, the "pOssibility Of hearing a
shadow fall upon i: piece Ut scleniunl."
Within the last few months he has succeeded
III putting this into practical execution,
III the artic,lating photopllone beam OF
light, derived either from an artificial source
or from the sun, is thrown by a mirror OIL to
the trallsmitter,. which is small disc OF
silverea glass, with tube and nouthplece
attached. The beam Of light reflected from
the tra1slnltter is focused us nearly as posi-
Bile upon the distant receiver. When, there
fore, words are spoken into the noutlpitce
the disc becomes agitated, alters slightly IN
shape, and, therefore, i'll its focal length, and
thus affects the receiylng-station by throwing
upon it a greater or less amount Of light, ac-
c0rding rs the beala is in or out Of focus. #
absolutely accurate adjustment were possi-
ble, and all disturbing elements could he
eliminated, the varying amount uf illulnilla-
ti0n received ut the distant end would wholly
depend upon the yariations III sound at the
transmitting end, and an exact reproduction
Of the original sounds would be obtained.
This we cannot expect yet, but the results
alreudy obtained lead one to hope that in
time even this may be achieved
The receiver OF the piotoplione, rs at pres
ent arranged, consists OF large concaye
mirror, which reflects and focuses the light
upon ascleniun cell; this is connected with Il
are included in tie circuit. Tie selenium
cell is very i11genionsly adapted by Prof.
Beti to its purpose. 1t consists of alternate
discs Of brass and mica, the edges Of which
are coated with seicnitlm, pared to make it
sufficiently large surface to the action OF the
light. Amy increase of light, falling npon this
Seiellium cell, lessons its electric resistance;
hence the vibrations Of the mirror (caused by
the words spoken into the nlonthpicce by the
Of light received upon the cell, reproduce
themselves audibly, by means Of the greater
or less amount Of electricity thereby trans
mitted through the telephone. Both trans
mitter and receiver must, Of course, he so
supported as to be free to move, accordin to
the direction in which the beam has to be
sent OF received.
There are many difficulties in the practical
working of this little Instrument, but though
ettMely satisractory results have not yet
been obtained, the principle is beyond dis
pure that sound and light can act upon one
another in the manner described. Articulate
speech has been transmitted by rneails of the
telephone to a distance Of sotne 20 yards,
loudly :ls in talking through an ordinary tele
phone, though tile sound varies in Intensity
III an unaccountable manner.
Prof. Bell has arrived ut many interesting
strument- lie has found tilat curious
molecular changes tnke place not only in
scleniunn, but also in thin surfaces ut almost
any substance; SO that they respond. by audi
ble vibrations, to the action of all interlnit~
ence, however, III the sensitiyeness Of tie dit-
ferent substances; vulcanite is one of the
best, carbon is very good, but water is abso-
lutely irresponsive, and glass, unsilyered, is
also bad: Upon this discovery, Prof. Bell
for transmitting musical tones.
q oea1ll OF light Is thrown upon mirror,
nlld focused by a lens as before; at the focus
is q disc, perforated round its circumference
Will I4OiCo. IlOll tuiS tll5E. WHICH
can bc rotated SO that the beau passes
through varying number of holes, accord
ing to the speed of rotation, the light passes
Oil to areceivlrg disc of ebonite. from whence
the sounds are conveyed by tube to the
listener. That these musical soNnds--which
are much louder than the spoken words-are
really due to the action Of light or radiant
energy of some form, may be easily
proved, for when the beam is Interrupted by
means Of a disc Of some opaque body, though
the perforated disc is still rotating, nothing is
heard at the receiver. No wires are needed
as conductors between the tr;ansnlitter and
the receiver; the beam Of light forms the only
necessary connection, and this beam of light,
Will the Simple apparatus described, hu3
been the means of conveying distinct musical
sounds to the distance Of more than mile Not
that even this distance is necessary limit,
for there is no reason why the sound should
not be carried as far rs the light can be
thrown. we have here, in fact, a 7n1tsicut
hetiDstat.
The real cause Of the molecular changes
accompanying this action of Ill intermittent
beam Of light upon different substances is
not yet certain. It appears probable, how
ever. that the varying electric resistaiices Of
selenlun are directly due to light; whilst,
as with the radioneter, radiant heat is prob
ably the real source Of those molecular
Changes which produce the audible vibra-
tons Of vu!canite and other bodies Whether,
however. it be heat or light which is the
original source of these vibrations, the Won !