Free trader-journal. (Ottawa, Ill.) 1916-1920, 1917-10-29
MOST WONDERFUL
LENS IN WORLD
sEARCHll6HT SENDS FORTH
BEAM AS BRILLIANT AS
FlERcEST SUNLIGHT.
You Can Read a Newspaper by Its
Rays Thirty Miles Away.

II is Ten lett hlEn, IT'S mirror mas
a diameter of five feet. and it weighs
three tons Its beam il as brilliant
or in the afternoon. New York lat
ltude. and YOU can read Il newspaper
by it's light thirty miles away. The
heat OF its focused beam is SO intense
that II will set paper afire at a dis.
lance of $50 feet II has a candle pow.
er of more than one and one quarter
billion.
These are few astonishing facts
about the Sperry searchlight. the in
yention OF Elmer A. Sperry of Brook
lyn, y. Y, who is already known as
the inventor OF the airplsne stabllizer
ant ship gyroscope bearing his name
ard the first electric arc light When
the last big air raid over LONDON
was made by Zeppelins, the Sperry
searchlights bathed the biz dirigihles
in beams OF light they could not es'
cape. According TO some London &C
counts the Sperry searchlight is the
Zeppelin Nemesis,
One OF the most powerful Deacons
along the coast is the Sandy Hook
lighthouse. But the Sperry search.
light is twenty-five times more bril-
liant than that light. Were The
Sperry lamp substituted for the light.
house beacon, a ship passing out to
sea could be bathed in light until it
disappeared below the horizon. BY
swinging the light back and forth
across the rky it has been made
visible $50 miles away. For navy use
the Spe,ry lamp eliminates tar.
get ten times more brilliantly than
any other protector devised.
Equipped with carriage that per
mits the lamp to be turned in circle
and in any direction up to 80 degrees,
the giant searchight is of the great
est value in detecting aircraft. The
operator cannot control it near at
hand; the great heat prevents that
He must stand fifty feet away, At
that distance he is able to focus ac-
curately upon any moving object. Be
cause the rays projected BY the lamp
are nearly parallel, there is no diffu
sion OF light over wide area. The
beam is concentrated.
When the searchlight Is being oper.
ated the temperature OF the arc is
5000 degrees Fehrenheit-7,O00 de.
grees higher than the melting point
of the metal holders OF the carbons.
Consequently, in order to prevent
these parts from melting. a current of
air is forced, by means OF motor
driven blower, through the carbon
supports and discharged through the
heat radiating disks that surround the
holders. In the Beck lamp the hold.
ers are sprayed with alcohol to pre-
vent them from melting.
The several factors which combine
TO make the Sperry lamp 50 powerful
are the small electrodes. the special
carbons used, the manner in which
they burn and the paraboic mirror. A
colored glass peepsight enables the
operator to watch the arc without be.
ing blinded by the glare, or the arc is
reproduced by lenses upon ground
glass outside the lamp. An iris dia'
phram, similar to that used in cam
eras, regulates the light.
Stand in the beams Of the Sperry
lamp at any distance closer than 500
teeL and your skin will be burned. AT
that distance The skin peels The
great heat OF the arc is due TO the
fact that it produces crater which
more nearly approximates the math'
ematical point OF light tan does that
in other searchlights, The candle
power is more than $780, 900 per square
inch.
Designed for naval and military pur-
poses, the Sperry lamp, in addition to
locating enemy forces on land and in
the air is useful also in throwing a
screen OF powerful light in front OF
the enemy II is impossible to see
through its concentrated beam Allied
field forces have mounted the lamp on
armored cars and have found it avail.
able for signaling at any distance up
to 100 miles.