, 1880-12-29
THE PHOTOPHONE.

~-
The world cannot keep pace with the
scientific surprises of this age. Before
sufficient time has elapsed to make n
startling invention familiar, another equal
ly astonishing is already the subject of
lectures and newspaper articles. Before
the telephone, the m~icrOphOne, and the
phonOgraph have found their way into
common use, a still more extraordinary
instrument is announced,-One of which
the results are unexpected by the scientific
as they are incredible to the ordinary mind.
We hear of conversation being carried on
by means of a trembling beam of light, and
incred ulity reaches it's climax when it is
whispered that the P%hOtOphOne may enable
us to hear the rise and fall of those gigan.
tic storms that are constantly sweeping
over the SUMS surface. Is it possible that
the revelations of modern Science-cOnS
demned as materialiStic and prOsaic-can
thus Outstrip the widest fights of the
Imagination: =, ...s,. v,,,.vp.
ment of Professor Graham Bells lngenul-
ty, and for it's scientific novelty, IT not for
It's practical utility, well deserves a brief
description. One of the elementary DO.
dies, named selenium, and allied to sulphur.
is known to undergo certain changes in its
molecular structure when light falls upon
it. These changes cause the very high
resistance it offers to the passage of an
electric current to vary slightly, and this
curious effect, hitherto believed to be
unique, has lately been the subject of
investigation by various English physicists.
1t occurred to several hat this substance
might be employed as a sort of telephone,
a beam of light being used to replace the
conducting wires of the usual forms OF
these instruments. Professor 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.
A mirror, from which is reflected q pow.
erful beam of light, may be caused to VI.
brate by means of the voice. These vibra.
tiOns toss the beam of light slightly to and
fro, and this vibrating beam falls upon a
selenium receiver, through which an cleo.
trio current is passing, thereby creating
slight variations in the resistanceS the
current encounters. These tiny variations
in electric resistance can be detected and
rendered audible by that wonderfully SEN
sitive little instrument. the Bell telephone.
This was the conception which led Pro.
fessOr Bell to announce, in a lecture de-
livered before the Royal Institution so long
ago as 1910, tuo 'pOSSiUiltJ "a -
shadow fall upon a piece of selenium."
Within the last few months, he has sue.
ceeded in putting this into practica! execu-
ton. M An ..
In the articulating photophone, q beam
Of light, derived either from an artificial
source or from the Sum- is thrown by q
mirror on to the transmitter, which is
a small disc of silvered glass. with a tube
and ~mouthpiece attached. The beam OF
light reflected from the transnaitter is TO-
cussed as nearly as possible upon the dis
tant receiver. When, therefore. words
are spoken into the mouth piece, the disc
becomes agitated, alters slightly in shape,
and, therefore, in its focal length. and thus
affects the receiving station, by throwing
upon it q greater or less amount OF light.
according as the beam is in or out OF focus.
If absolutely accurate adjustment were
possible, and all disturbing elements could
be eliminated, the varying amount OF lila.
mination received at the distant end wonld
wholly depend upon the variations in sound
at the transmitting end, and an exact re.