Using the Machine.—­The rod support, paper, and sitter should be arranged so that the rod is level at the height of the sitter’s nose and the pencil on the centre of the paper.  Bring the support near enough to the paper to drive the pencil back into the tube until the point projects only half an inch.

A thread attached to the pencil will enable you to keep the pencil off the paper until you wish to begin drawing the profile.

Begin with the pointer pressing against the sitter’s chest, and bring it over the face and down the back of the head and neck.  Do not press it into the hair, but carry it along what you consider to be the outline; though it must be in actual contact with the features and clothes.  It is hardly necessary to mention that the sitter must keep perfectly still if the silhouette is to be at all accurate.

The tracing is cut round with fine-pointed scissors, and the paper blacked and stuck on a piece of white card.  Some trouble is saved by using paper white on one aide 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.