a sharp
pointed knife. If you have a jig saw, you can make a bromide
enlargement from the negative you have selected and mount the
print on a smooth board that is not too thick. This wood-mounted
picture can be sawed out making all shapes of blocks, which forms
a perfect jig-saw puzzle.
--Contributed by Erich Lehmann, New York City.

** Rolling Uphill Illusion [361]

This interesting as well as entertaining illusion, can be made by
anyone having a wood-turning lathe. A solid, similar to two cones
placed base to base, is accurately turned in a lathe, the sides
sloping to an angle of 45 deg. The spindle can be turned out of
the solid at the same time as the cone; or, after turning the
cone, drive an iron or wood shaft through the center making a
tight fit.

The boards for the track are made with a sloping edge on which the
cone is to roll. This slope will depend on the diameter of the
cone, which can be any size from 3 to 12 in. The slope should not
be too flat, or the cone will not roll, and it should be such that
the

[Illustration: The Illusion]

one end will be higher than the other by a little less than half
the diameter of the cone. Thus it will be seen that the diameter
of the cone determines the length of the slope of the tracks. A
notch should be cut in the tracks, as indicated, for the shaft to
drop into at the end of the course.

The lower end of the tracks are closed until the high edge of the
cone rests upon the inside edges of the tracks and the high end
spread sufficiently to take the full width of the cone and to
allow the shaft to fall into the notches. When the cone and tracks
are viewed from the broadside the deception will be more perfect,
and will not be discovered until the construction of the model is
seen from all sides. Should it be difficult to make the cone from
wood, a good substitute can be made from two funnels.
--Contributed by I. G. Bayley, Cape May Point, N.J.

** Annealing Chisel Steel [362]

Persons who have occasion to use tool or carbon steel now and then
and do not have access to an assorted stock of this material find
that the kind most readily obtained at the hardware store is the
unannealed steel known as chisel steel. Machining or filing such
steel is exceedingly slow and difficult, besides the destruction
of tools; as a matter of fact this steel is intended for chisels,
drills, and like tools which require only forging and filing. If
this steel is annealed,