The record-union., 1898-07-31
SEARCHLTGHT PROTECTION.
The Most Powerful Searchlight il
the World for San Francisco.

The Government has recently secured
the most powerful electric searchlighJ
in the world for the entrance to San
Francisco Bay, to be used in the pro-
lection of our western outpost in case
OF possible attack. The wisdom of this
action on the part of the Government
Will be conceded in view Of the possi-
bility of international complications re-
sulting from the war
The light from this great protector is
conservatively calculated to be equal to
that of not less than 315.0O0,OOO can
dies. The distance from which it can
be seen is considerably over 100 miles,
and moving objects can be detected by
its light almost as far as marine glasses
can carry.
1t stands 10 feet 6 inches high TO the
top of the drum, and the total weight
IS about 5000 pounds, but so perfectly
IS il mounted and balanced that child
can move it in any direction. 1t was,
built by the General Electric Company
Of Schenectady
The rejecting mirror used is con-
cave spherical mirror, five feet in diam
eter, rejecting parallel beam of light
1t was manufactured especially for this
protector and is specimen of perfect
optical work, three and one fourth
inches thick at the edges and one-siX-
teenth Of an inch thick at the center
1t weighs about 500 pounds. The metal
ring IN which it is mounted weighs
ABOUT 100 pounds, and the total lens
ring and cover, weigh about iG0O
pounds This great mirror is mounted
at one end of the big drum, the outer
end Of which is furnished with door
consisting of a number of plate glass
strips. Inside the drum and slid
ing upon ways arranged on the bot
tom, is placed the electric arc lamp,
the source Of the light which is re-
Hected by the mirror. 1t is entirely au-
tomato in its action, is six feet high,
weighs about 400 pounds. The car
bons used are also made especially for
1t. The upper or positive carbon is one
ana one-half inches in diameter and
twenty-five and one-half inches long
The lower or negative carbon is one and
one-fourth inches in diameter and tif-
teen inches long. The outer surfaces
OF the carbons are heavily coated with
copper The positive carbon is set q
little IN front of the negative and thus
almost all the intense light of the in
candescent crater of the are is cast
upon the reflector
Al the maximum current at which
this lamp operates 1t has a luminous
intensity of about 10000 to 100 900
candles-the reflected beam a total lu-
minous intensity of about 315, coo 900
candles, an intensity which the eve
cannot appreciate. In looking at the
side of the beam the spectator only dis.
tinguishes a stream of light Of COM
paratively low intensity, but in looking
at the beam directly the effect is abso-
lutely binding. Ventilators at the top
and sides allow a constant current of
air TO pass through the drum and dis
sipate the heat generated by the arc
lamp, and they are 50 arranged that
no light can escape through them To
confuse the operator. All the connec-
tions for adjusting the positions Of the
carbons and the lamp are brouph.
through the drum to the outside and
are arranged in close proximity to one
another at one side so that all NAV no
manipulated by the operator without
moving from his position Through
openings in the drum covered by dense
ly colored glass the operation of the
lamp may be watched. and its adfust-
ments made. The drum is supported
in bearings at the top of a Y-shaped
fork, set in a base plate, running on
small wheels, forming turntable, rest
ing upon massive pedestal supporting