Evening star., 1925-09-20

Early in the World War a new
means Of practically secret signaling
was developed by a number of Amer
lean engineers and representatives of
the Army and Navy. 1t was first
termed infra-red signaling. but later
came to be known as "dyscra site
1t is not radio, but operates through
the medium Of infra-red light waves,
which are invisible to the eye. AS a
conventional vacuum tube receiver is
used for reception and amplif1cation of
signals. and because a telegraph key
or telephone apparatus is employed
to control light beam, the system of
communication may be of interest to
radio fans
In the Fall Of 1916, T. w. Case of
the Case Research Laboratories dis
covered and reported upon the pecu-
liar properties of lead antimony sui.
phide, when the long red rays Of the
spectrum fell upon a crystal Of this
chemical. First it was tried out in
detecting the approach of electric
cars. or rather detecting their power
ful headlights, In New. Auburn, n. Y.
In This hrst experiment the tests
showed results at a distance of about
3oo rect. Refinements, however, with
better lights, filters and electrical gal.
vanometers. increased the range to
ABOUT a mile. The Sperry people be-
came interested and further tests fol-
lowed under the observations of Army
and Navy officers, who evinced In
terest in connection with the possi-
bility of secret signaling in battle
and at sea. A 2-mile test was sue
cessfully conducted both at night and
In daylight between the Sperry Build
Ing and the Woolworth Tower, and
upon reports of this rccess in 1917
Gen. Squier. chief signal officer of the
Army, suggested a 10-mile test.
II was this mere military trial which
led to the desire for making the re-
cetved signals audible. and special
vacuum tubes were developed. 1t was
found that the pitch of the received
signal note varied In wireless head
phones with the intensity Of the light
or the hitter. The ultimate distance
reached with this improved means
was about miles.
England became interested, and
Lord Northcliffe witnessed a demon
stration, following which he expressed
a belief that 1t might serve in front
line trenches as q means of secret
signaling.
Later. further tests carried the
range to IS miles or from Fort Han
cock. in New York Harbor, to the
Woolworth Building, and another test
indicated good reception Of signals
from the shore to vessel at sea.
The Navy, Department, in discussing
the possibilities, reported that it might
serve as a method Of invisible signal
ing between the vessels of a CONVOY
proceeding without lights. and that it
would probably be valuable in aiding
vessels to locate their positions off
shore without using radio. The chief
use to the Navy. however, appeared
to be as means of secret communica-
ton, when vessels were proceeding
without lights or In battle. It's radius
of action was found to be about II
miles, while the cost Of a complete set
was comparatively low-about $40O.
This system, although not now in
practical use, Is not discarded-far
from 1t. 1t has been termed black
RADIO" and several other strange and
suggestive, names. One of it's impor-
tant features is that it Is directional,
more like beam radio than, pure radio
broadcasts.
In recent dyscrasite communication
tests light rays are generated by an
incandescent lamp, although a gas
flame. and an arc light have been
used. The light is situated in front Of
parabolic mirror by means of which
the divergence CT the beam is con-
troiled. The whole apparatus is
housed in lightproof case. with an
opaque screen which permits only the
invisible infra-red rays to pass out of
the transmitter. Telegraphic signals
are made by means Of shutter oper-
ated by a hand key. This shutter is
located either outside the case or be-
tween the light and the mirror.
Telephone impulses may be con-
verted into light values by speaking
against a drum controlling the gas
supply. in the gas-fame system, which
varies the gas pressure and modulates
the light according to voice variations
At the receiving end of the circuit,
detection Is accomplished at present
by inserting piece Of crystal, super
sensitive to infra-red rays, at the
focus of a parabolic reflector. The
crystal forms part Of a conventional
vacuum-tube circuit. Variations in the
incoming infra-red rays impinging on
the crystal alter the constants Of the
vacuum-tube circuit and produce vari-
ations audible in either head phones
or a 1oud-speaker.
Recently perfected dyscrasite trans
mitters are highly directional, hav-
ing only an 8-degree divergence Of
beam, which makes for secrecy to
a certain extent, although limiting its
in general communications.
Another limitation Of this apparatus
is the fact that 1t Is practical only for
night signaling, the infra-red rays of
the bright sunlight overshadowing it's
impulses and paralyzing the detec-
tive elements. At night. however, 1t
forms the only known means Of COM
munication not subject to reception
by ordinary means, such as visual,
radio or sound detection, which indi.