tch shows two optical illusions, the first
having a perfect circle on the outside edge

[Illustration: The Two Illusions]

appears to be flattened at the points A, and the arcs of the
circle, B, appear to be more rounding. In the second figure the
circle appears to have an oval form with the distance from C to C
greater than from D to D. A compass applied to the circles in
either figures will show that they are perfectly round.
--Contributed by Norman S. Brown, Chippewa Falls, Wis.

** Use of Kerosene in Polishing Metals [364]

Anyone who has polished a flat iron or steel surface with emery
cloth knows how soon the cloth gums and fills up. The cloth in
this condition will do little or no cutting. A simple remedy for
this trouble is to use kerosene on the surface. The oil floats
away a large part of the gumming substance and leaves the emery
cloth sharp and clean to do the best work, also, it seems to act
as a lubricant to keep particles of metal from collecting on the
cloth and scratching or digging in the surface of the metal. A
very light lard oil is equally good for this purpose, but not
always easily obtained. A surface polished where oil or kerosene
is used does not rust so easily as one polished dry, for the
reason that a little oil remains on the metal.

Kerosene is the best to use on oil stones, being better than
heavier oil. This oil readily floats away all particles of the
feather edge that are liable to become loosened and forced into
the stone. These particles of metal when stuck to the stone are
the cause of spoiling it, as well as nicking the tools that are
being sharpened. Keep the surface of the stone well oiled at all
times to make the cutting free.
--Contributed by Donald A. Hampson, Middletown, N. Y.

** How to Make Lamps Burn Brightly [364]

For a good, steady light there is nothing better than a lamp, but
like most everything it must have attention. After cleaning well
and fitting it, place a small lump of camphor in the oil vessel.
This will greatly improve the light and make the flame clearer and
brighter. If there is no camphor at hand add a few drops of
vinegar occasionally.

** A Practical Camera for Fifty Cents [365]
By C. H. Claudy

I say for fifty cents, but really this is an outside estimate. If
you possess a few tools and the rudiments of a shop, by which is
meant a few odds and ends of screws, brass and nails, you can
really make this camera for nothing.

The c