The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1919-09-21

|
IAN right. Go ahead" 1 shouted.
Then the counting started. zone, two
three, four" Each word was perfectly
distinct.
Five, six, seven, eight These words
not spoken into the telephone came with
blurred sound through the closed door.
The difference was NAKED.
Then sharply and clearly through the
telephone came the completion of tho
numbers.
You can whistle through it just as
WELL" DR.. Rankine assured me. And he
gave me a convincing proof For the first
time in my life I had been spoken to
and whistled for along beam of light.
This is how it works: The light, wheth-
err sunlight or searchlight, is reflected
through lens and then grid on to
the concave mirror. When anyone speaks
INTO the trumpet the sounds are collect
ed by a gramaphone sound box. The
sound box needle vibrates in accordance
with the sounds. AS the mirror Is fixed
to the needle the mirror vibrates, too
The image of the first grid is reflected
from the mirror on to the second which,
being milled with the first, is an exact
reproduction of it but inverted. So when
the mirror vibrates it sends the gridded
| light against the second grid and &C.
cording to the sounds made is the pro-
portionate amount of light that goes
through the grid. So you have shut
ter light effect just like shutter sig
mailing.
| This light is trained by means of the
gun sights on the mirror of the receiv-
| ing instrument. The mirror concentrates
| the light on the selenium cell. Selenium
is sensitive to light. Its power of con-
Quoting electricity varies with the inten-
sity of the light thrown on it. The grid,
| acting as a shutter, varies the light
intensity in correspondence with the
movements of the mirror attached to the
sound box The electric battery and the
telephone ear piece receiver do the rest
| In this way speech has been sent over
beam of light a distance of mile
and a half. The tests, owing to war
conditions, have been limited. AS far az
the inventor can tell there is nothing to
| limit the distance over which messages
! can be sent except the limit of mutual
visibility At sea it should be possible
in bright sunlight to send them from
horizon to horizon. On land the dis
lance should be as far as light can travel
without interruption. In photography 70
miles is the longest distance attained.
This was in the Wagiri expedition of
1881 with a fve-inch mirror. But there
is no present prospect of the sunphone
reaching out so far as that. 1t is GER
tain to be effective for eight miles. How
much further it may be practical to
experiments were carried out under war
conditions. 1t was necessary to keep
the secret. Long distance experiments
were outside the scope OF secrecy. SO
the instrument while brought to perfect
accuracy for short ranges, has yet to be
tested for long ones.
This is what the inventor says about
it: ut has proved to be practical and
reliable means of transmitting speech
y.zLL RI a.
half miles have been achieved, in spite
of the fact that, owing to war condi-
tions it has not yet been possible to
construct the apparatus in its most con-
venient form. There appears also to be
room for considerable Improvement IN
the selenium cells which have been used
as receivers and it is quite probable that
the range can be increased to several
miles,"
The great advantage Of the sunphone Is
that messages can only be tapped -
anyone getting in the way of the beam
of light This would be obvious to those
using the instrument at once. AS II
could be so easily detected it would not
be worth while attempting 1T. Wireless
telephone messages are easily tapped 1t
is only matter Of finding the right key.
You can also Join wireless" But you
cannot join sunlight. 1t is easy to inter
cept a beam of light, of course YET
it, would be risky. To do it would mean
getting in between in the direct line OF
light 1t would mean instant discovery
and trouble to follow. That is the only
way YOU can tap the sunphone. No one
can overhear conversations over 1t. II
is quite safe and quite secret. Safer
and more secret than wireless though
rot of course comparable to 1t in range
The sunphone is superior to the heno-
graph as it needs no code.
The idea of using light as vehicle
for speech is not new. The way by
which the problem has been solved ir
new That is all, but 1t is everything
! II all hangs around selenium. Selen
ium is an element of the sulphur group
Its chief source is the flue dust obtained
in burning pigrites in the making of sui
phuric acid by the leaden chamber pro
cess. 1t is a gray, crystalline, semi me
tallic substance It's chief property is 1T
response to light 1t conducts electricity
as I have already explained. in proper
ton to he brightness Of the light which
! = brought to bear upon it, This char
stic has long besn well known Fol-
asst 30 or 40 years various attempt.
have been made to use it for the pun
pose to which Dr. Rankine has now man
aged to apply it.
1t is an interesting fact that Selene wa:
the moon goddess of Greek mythology
She was sister to Phoebus, the sun god
and rode across the heavens In chario
1 drawn by two white horses. In view Of
| DR. Rankine's discovery who will say
| that tselenium is not we'll named?
| Two main methods of solving this prob
lem of speech transmission by light have
| been tried by previous experimenters
| One was to cause fluctuations varyine
with the sounds Of speech in the source
: Of the light itself The other was to pro
4 duce the fluctuations varying with thu
: sounds of speech in the source OF thu
d light itself The other was to prcfuc'
e the fluctuations indirectly by causing thu
5 speech to interrupt the light after 1T hat
: left its source. The second is the on
: used by DR. Rankine. Bv using this n
lis able to EMPLOY SUNLIGHT as well a
n artificial LIGHT. If he had kept to tn
Il other method SUNLIGHT obviously could no
: have been used. The average freouenc!
$ of speech sounds is about 500 per sec
. . ond That means that the brightness o
e the beam Of light must alternate between
Il maximum and minimum every one Ave
hrndredth of second.
h GRAHAM BELLS EXPERIMENTS
I. "In patent specification of 1889 Ora
n ham Bell describes two Devices" writes
r DR.. Rankine in his paper. In the frs
d the proposal is to allow the beam O.
k light to pass in succession through two
grids consisting of equal parallel strip
\ alternately opaque and transparent. On.
4 of these is fixed in position and the othel
Is moved bodily in = direction perpendic