The Ketchum keystone. [volume] (Ketchum, Idaho) 1885-1899, 1893-10-14
THE RADIOPHONE.
Talking Through Space by Means
OF Heet Rays.
A Wonderful Invention OF Prof. Bells on
Exhibition at the Worlds Fair
How the Instrument Is
Worked.

sation is transmitted through space on
a ray of light, no wires or electricity
being used in any portion of the appar-
atus, is one of the scientific wonders at
the worlds fair. The photophone, by
which a telephone is caused to re-
spond to the variations in intensity of
light ray falling upon selenium
cell placed in local electric circuit is
familiar. Prof. Alexander Graham
Bell succeeded in transmitting articu-
late speech in this way by making a
beam of light, which mirror reflects,
vibrate, the vibrations being OF the
same kind as those produced by speak
ing through a membrane. He used a
thin mica or glass plate as a diaphragm,
which by being silvered served at the
same time as mirror. The reflected
ray of light as it fell upon the selenium
cell at the distant point varied in in
tensity in unison with the sound waves
which caused the vibration of the dia-
phragm mirror. The varying intensity
of thu light produces in the selenium
cell corresponding variation in the
resistance of the local circuit, and the
VARYING current which results there
from is translated into sound waves by
the telephone, which correspond exact
ly with the sound waves which vibrated
the diaphragm.
Prof. Bell pursued his Investigations
looking to obtaining sounds without
the addition of a local circuit, and his
latest production, that which is now
about ready for exhibition in the Bell
telephone pavilion in Electricity build
ing, may be briefly described as fol-
lows: In the northwest gallery, over
hanging the main floor few feet,
there has been erected small plat
form, upon which the sending appa-
ratus is placed This consists of a
focusing arc lamp of ordinary pattern,
whose rays. rendered parallel by lens,
are reflected from thin diaphragm
mirror to the receiving instrument
about eighty or ninety feet away, at
the north front of the Bell telephone
pavilion. Tue rejecting mirror is q
disk of very thin glass, silvered on its
reverse side and held in heavy brass
frame by means of washers Of ordinary
blotting paper. Opening into the
chamber in the rear Of this mirror is
an ordinary speaking tube, into which
the sounds are uttered, causing the
mirror to vibrate as would the dia-
phragm of telephone transmitter.
These rays, reflected in parallel
lines, are received at the farther end
by parabolic reflector, in the focus OF
which is placed glass bulb, contain
ing a small portion of ordinary burnt
cork The bulb is blown into the end
of glass tube about a quarter of IN
inch in diameter and four inches long,
the other end of which is open, and to
which is attached an ordinary phono-
graph hearing tube, which extends
into a small cabinet, where the liste-
ner. removed from external noises, re-
ceives 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 parabOlic
reflector, and that the bulb containing
the burnt cork be brought to the focus
of the parabo!ic mirror. This latter is
accomplished by pushing the glass
tube in or out until satisfactory re-
suits are obtained. Certainly nothing
could be simpler than this; but, al
though the instrument is Of great sci
entific interest, it has no apparent
practical value. The transmitted
words, as heard through the hearing
tubes, lack sharpness of definition and
have somewhat muffied 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 ex-
preston for which one was not pre-
pared Prof Bell has given the fol-
lowing explanation Of the philosophy
Of the phenomenon: When the inter-
mittcnt beam strikes upon the re-
ceiver. the particles are alternately
heated and cooled; when they are
heated they expand, and consequently
the intervals which are filed with air
are diminished; when the light is inter-
cepted the particles are cooled and the
spaces between them enlarged. Air is
squeezed out from the interstices be-
tween the particles in the first case
and drawn in in the latter; the enlarg-
ing 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 con-
densation 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 al
ternately increased and diminished.
BY these means alternate waves of
compression and rarefaction are pro-
duced in the surrounding air, and it is
to this that the sound which is
emitted owes its existence.