Evening star. [volume] (Washington, D.C.) 1854-1972, 1908-08-09
THE MODERN SEARCHL|GHT
THROWING A BEAM OF BRIL-
LIANT LIGHT THREE MILES,
Various Uses to Which PROJECTORS
Are Put in the Navy-Long-
Distance Signals.
From the Literary Digest.

From the Literary Digest
The use of the "searchlight'' or pro-
Jector has now become almost universal.
1t Is used for picking up" an enemv.s
snip at night. for signaling in the army
ana navy, and for target practice: for
etereopt1cen illumination, theater illumf-
nation. scenic effects, electric headlights
Tor locomotives. advertising and for nu-
merous other purposes. says A. H. Kele-
her. writing on the subject in the Him.
minating Engineer.
"A searchlight consists essentially Of q
focusing CLAMP mounted in a cylindrical
box provided with a reflector and me-
chanical accessories for sending the
beams so obtained in the required d.
rection. The lamp consists ri
the arc-light, with which we are SO IA
miliar In connection with the lighting of
our streets.
Parabolic Mirror.
The purpose of the parabolic mirror.
used In connection with the searchlieht.
is to gather up the light-rays coming
from the carbon arc and redirect them
In the required direction. The word
'parabolic' indicates the shape of the
mirror. BY placing light source in the
focus Of a parabolic mirror, reflected rays
are thrown of. and all of these rays are
Theoretically parallel to each other This
Is not the case in actual practice, how
ever. as owing to dispersion due to the
size OF the source. atmospheric absorp-
tion and other causes, the beams are not
truly parallel.
Small colored glass windows are
provided to correct for the wan
derfng OF the arc from the focal posi-
tion 1t Is, Of course. important to keep
the arc. at the focus Of the mirror. be-
lisht-rays will not be parallel and con-
sequently the protector will not have the
maximum possible range which in the
case OF good lights varies from 1000 to
10000 yards.
When large searchlights with mirrors
having great diameters are used, 1t be-
comes necessary to use some form of
power to operate the turning gear OF the
searchlight For this purpose there are
used a vertical wheel and chain operated
by an electric motor, which turns the
barrel Of the searchlight around its hori
xontal axis. and a motor driven revolv-
Ing base, which allows the light to be
turned from. one point Of the compass to
different speeds so that the light may
be used in different classes OF work. For
instance. q searchlight intended for use
on a warship or in a fort must have a
very versatile turning gear. while q
searchlight used on shore for minor pur-
poses need only be worked by hand. as
the light is directed on the target and
allowed to stay.
1.-The glass door of the protector barrel
Is composed Of strips of plate glass. This
window is included to protect the search
light mechanism from the wind and rain.
and is made of strips SO that 1t will not
crack from the effects Of heat. broken
strip can be easily removed and new
one inserted In it's place. These nat
strips are at times replaced by lens strips.
the surfaces Of which ara rounded In or
der to make the light-rays diverge. which
condition is sometimes desired. This di-
yergence OF the rays could also be Sc
cured by removing the arc slightly from
the focus OF the mirror"