If the apparatus works stiffly, ease the holes a trifle and lead-pencil the wood at all points where two surfaces rub.  It is absolutely impossible to make a good reproduction with a stiff, jerky pantograph.

To decide the positions of original and the paper for the copy, get the pointer centred on the original and adjust the paper till its centre is under the pencil.

XXXVII.  A SILHOUETTE DRAWING MACHINE.

With this very simple apparatus you will be able to give good entertainment to such of your friends as may wish to have black paper records of their faces in profile.

The machine is merely a long rod, with a sliding pencil attached to one end and a metal pointer stuck into the other, supported near the pencil end on a pivot which permits free movement in all directions.

For heads and busts only, the rod and pointer combined need not be more than 4 feet 6 inches long.  The rod is a 1/2-inch blind rod, the pointer a stout knitting-needle driven axially into one end of the rod.  This pointer, being of small diameter, follows the minor curves and angles of the features much more closely than would be possible with the rod.

The support is a piece of wood, 1-1/2 inches square and 12 to 15 inches long, screwed on to a large foot, which should be fairly heavy, as any tilting or slipping will, of course, spoil the silhouette.  The universal joint for the rod is made by soldering a small U-shaped piece of metal to the end of a short metal bar.  The ends of the U are drilled for a pin passing through the rod; and a hole is sunk into the top of the support to take the bar.  The fit should be close, to prevent the pivot rocking about, and the hole in the support deep enough to bring the bottom of the stirrup down against the wood.

If a series of holes half an inch apart is drilled, through the rod, the nearest 9 inches from the pencil end, the size of the silhouette proportionately to the original can be varied by moving the pin from one hole to another.

[Illustration:  Fig. 188.—­Silhouettograph in use.]

[Illustration:  Fig. 188a.—­Group of silhouettes drawn with the machine described.]

The pencil holder is 4 inches of tubing, in which the pencil can slide easily without shaking.  If necessary, the size of the pencil should be reduced by rubbing with glass paper.  Bind the holder tightly to the end of the rod away from the pointer, so that one extremity just overhangs the rod.  A piece of thin elastic is tied to the unsharpened end of the pencil and to the pencil tube, the adjustment allowing the pencil to project an inch when the elastic is taut but not stretched.

A fairly soft pencil and a thick, smooth paper or card give the best results.  Paper should be backed by something hard to prevent the pencil digging in.  Attach the paper to a firm vertical surface, such as the side of a box, a drawing board, a wall, etc.