n completing

[Illustration: Interior View]

the circuit the core will descend; or put in a switch or push
button on one of the battery wires. If the button be concealed
where the operator can reach it, the core will obey his command to
rise or fall, according to his control of the current. This is a
mysterious looking instrument, the core being moved without
visible connection to any other part.

** Lubricating Sheet Metal [69]

To lubricate sheet metal mix 1 qt. whale oil, 1 lb. white lead, 1
pt. water and 3 oz. finest graphite. Apply with a brush before the
metal enters the dies.

** An Optical Top [69]

One of the latest optical delusions, and one not easy to explain,
is Benham's color top. Cut out the black and white disk shown in
the figure, and paste on a piece of stiff cardboard. Trim the
edges of the cardboard to match the shape of the disk, and make a
pinhole in the center. Cut the pin in half and push it through
from the under side until the head of the pin touches the
cardboard. Spin slowly in a strong light and some of the lines
will appear colored. The colors appear different to different
people, and are changed by reversing the rotation.

[Illustration: An Optical Top]

** Card Trick with a Tapered Deck [70]

Another simple trick to perform but one not easily detected, is
executed by using a tapered deck of cards as shown in Fig. 1. A
cheap deck of cards is evened up square, fastened in a vise and
planed along the edge in such a manner that all the pack will be
tapered about 1/16 in. This taper is exaggerated in the
illustration which shows

[Illustration: Cards from a Tapered Deck]

one card that has been turned end for end.

It is evident that any card reversed in this way can be easily
separated from the other cards in the pack, which makes it
possible to perform the following trick: The performer spreads the
cards out, fan-like, and asks an observer to withdraw a card,
which is then replaced in any part of the pack. After thoroughly
shuffling the cards the performer then holds the deck in both
hands behind his back and pronouncing a few magic words, produces
the card selected in one hand and the rest of the pack in the
other. This is accomplished by simply turning the deck end for end
while the observer is looking at his card, thus bringing the wide
end of the selected card at the narrow end of the pack when it is
replaced. The hands are placed behind the pack for a doubl