ide and black on the other. If duplicates are needed, two or
more pieces of paper should be stuck together by the corners and to the
paper on which the silhouette is drawn, and all be cut through at one
operation.

With a little practice the actual tracing of the outline occupies but a few
seconds. Things are expedited if an assistant adjusts the paper and pencil.

XXXVIII. A SIGNALLING LAMP.

Visual signalling is effected at night in the Morse code by means of a lamp
fitted with an easily-moved shutter, which passes or cuts off the light at
the will of the operator. Readers who know the Morse code might well go to
the trouble of constructing in duplicate the simple apparatus to be
described, as the possession of an outfit will enable them to extend their
signalling capabilities.

The stand for the lamp is admirably supplied by the ordinary camera tripod.
For the illuminant we may select any good acetylene cycle lamp.

For this a holder is made of 1/2-inch wood, according to the sketch shown
in Fig. 189. The width of all the four parts should be about 2 inches
greater than the front glass of the lamp. B and C should be sufficiently
far apart to allow the lamp to rest on the rim above the carbide chamber;
and the front, A, should be at least an inch higher than the top of the
lamp glass.

[Illustration: FIG. 189.--Signalling lamp with quick-moving shutter.]

The hole cut in B must be so situated as to bring the front of the lamp
close to the front of the holder, so that the greatest possible amount of
light may be utilized. The hole in A should be rather larger than the lamp
front, and, of course, be accurately centred. Mark these two holes off
carefully, and cut out with a pad saw or fret saw.

A socket must be attached to the centre of the underside of the base to
take the camera screw; or, if such a socket is not easily obtainable, a
hole should be drilled in the base to take an ordinary wood screw of good
size, the surplus of which is cut off so as not to interfere with the lamp.

The Shutter.--The woodwork is so simple that nothing further need be said
about it. The more difficult part of the business is the making of the
shutter, which must be so constructed that it can be opened and closed
rapidly by motions similar to those used in working the telegraph key
described in a preceding chapter. Speed of working is obtained by dividing
the shutter into two or three parts, each revolving on its own spindle,