ng Tinware [347]

New tinware rubbed over with fresh lard and heated will never
rust.

** Another Optical Illusion [348]

After taking a look at the accompanying illustration you will be
positive that the cords shown run in a spiral toward the center,
yet it shows a series of

[Illustration: The Cord Is Not a Spiral]

perfect circles of cords placed one inside the other. You can test
this for yourself in a moment with a pair of compasses, or, still
more simply, by laying a point of a pencil on any part of the cord
and following it round. Instead of approaching or receding from
the center in a continuous line, as in the case of a spiral, you
will find the pencil returning to the point from which it started.

** Substitute for Insulating Cleats [348]

In wiring up door bells, alarms and telephones as well as
experimental

[Illustration: Insulators]

work the use of common felt gun wads make a very good cleat for
the wires. They are used in the manner illustrated in the
accompanying sketch. The insulated wire is placed between two wads
and fastened with two nails or screws. If one wad on the back is
not thick enough to keep the wire away from the support, put on
two wads behind and one in front of the wire and fasten in the
same manner as described.

** Electrically Operated Indicator for a Wind Vane [348]

The accompanying photograph shows a wind vane connected with
electric wires to an instrument at considerable distance which
indicates by means of a magnetic needle the direction of the wind.
The bearings of the vane consist of the head of a wornout bicycle.
A 1/2-in. iron pipe extends from the vane and is held in place by
the clamp originally used to secure the handle bar of the bicycle.
In place of the forks is attached an eight-cylinder gas engine
timer which is slightly altered in such a manner that the brush is
at all times in contact, and when pointing between two contacts
connects them both. Nine wires run from the timer, one from each
of the eight contacts, and one, which serves as the ground wire,
is fastened to the metallic body. The timer is set at such a
position that when the vane points directly north, the brush of
the timer makes a connection in the middle of a contact. When the
timer is held in this position the brush will make connections
with each of the contacts as the vane revolves.

The indicating device which is placed in a convenient place in the
house consists of

[