The Portland daily press., 1893-09-19
SPEECH SENT BY HEAT RAYS.
A Wonderful Instrument, But Only Ex-
detrimental
[Boston Transcript

lBoston Transcript
Bells radiophone by which conversation
is transmitted through space on ray OF
light, no wires OF electricity being used
in any portion of the apparatus, is one
of the scientific wonders at the worlds
Fair. The photophone by which
telephone is caused to respond to
the variations in intensity OF a
light ray falling upon a selenlum cell
placed in local electric circuit is famil-
lar Professor Alexander Graham Bell
succeeded in transmitting articulate
speech in this way by making beam OF
light, which mirror reflects, vibrate,
the vibrations being Of the same kind as
those produced by speaking through
membranes. Housed a thin mica or glass
plate as diaphragm, which by being
silvered served at the same time as
a mirror. The reflected ray OF light as 1t
fell upon the selenium cell at the dis
lance point varied insintensity in unison
with the sound waves which caused the
vibration of the diaphragm mirror The
varying intensity of the light produces
in the selenium cell a corresponding
variation in the resistance OF the local
circuit, and the varying current which
results therefrom is translated into sound
waves by the telephone, which correspond
exactly with the sound waves which
vibrated the diaphragm. Professor Bell
pursued his Investigations looking to OBJ
tanning sounds without the addition OF
local circuit and his latest production,
that which is now about ready for exhl-
bition in the bell telephone pavilion in
electricity building, may be briefly de-
scribed as follows: In the northwest
gallery, overhangipg the main floor few
feet, there has been erected a small plat
form, upon which the sending apparatus
is placed. This consists of focusing
arc lamp of the ordinary pattern, whose
rays, rendered parallel by a lens, are re-
fiected from thin diaphgram mirror to
the receiving instrument about eighty or
ninety feet away, at the north front of
the bell telephone pavilion. The reflect
ing mirror is disk of very thin glass,
silvered on its reverse side and held in a
heavy brass frame by means of washers
of ordinary blotting paper Opening in
to the chamber into the rear of this
m rror is an ordinary speaking tube, in
toiwhich the sounds are uttered, causing
the mirror to vibrate as would the
diaphragm of telephone transmltter.
These rays, reflected in parallel lines, are
received at the farther end by parabollc
reflector, in the focus OF which is placed
ROA
ordinary burnt cork. The bulb is blown
into the end of glass tube about
quarter of an inch In diameter and four
inches long, the other end of which is
open, and to which is attached an ordl-
nary monograph hearing tube. which
extends into small cabinet, where the
listener, removed from external noises,
receives the message. The only adjust
ments required are that the rays be
directed from the mirror in the gallery in
an axial direction into the parabollc
reflector, and that the bulb containing
the burnt cork he brought to the focus
of the parabolic mirror. This latter is
in or out until satisfactory results are OBJ
tanned Certainly nothing could be
simpler than this; but although the in
strument is of great scientific interest, it
has no apparent practical value. The
transmitted words, as heard through the
hearing tubes, lack sharpness of defini-
ton and have somewhat muffled sound,
which is probably due to the tube
effects. The conversation can, however
be fairly understood if one knows before
hand what is to be expected, but it would
be difficult to follow an expression for
which one was not prepared. Professor
Bell has given the following.ex plantion OF
the philosophy of the phenomenon. When
the intermittent beam strikes upon the
receiver, the particles are alternately
heated and cooled: when they are heated
they expand, and consequently the inter
walls which are filled with air are dimin-
ished; when the light is intercepted the
particles are cooled and the spaces be-
tween them enlarged. Air is squeezed
out from the interstices between the par
ticles in the first case and drawn in in
the latter; the charging of the intervals
causes refraction of the air in the cork
particles, and the outer air rushes in;
the contraction of the interstitial spaces
causes condensation and escape of the air
they contain These two effects are still
further increased by the heating and
cooling of the air in the intervals alter
nately increased and diminished. By
these means alternate waves of compress
ion and rarefaction are produced in the
surrounding air, and it is to this that the
sound which is emitted owes its exist
ence