Simple as this model may seem in design, one built by the writer on exactly
the lines given has met the most famous flying models of the day in open
competition and proved successful against them.
XXVI. APPARATUS FOR SIMPLE SCIENTIFIC EXPERIMENTS.
Colour Discs for the Gramophone.--The gramophone, by virtue of its table
revolving at a controllable speed, comes in useful for a series of optical
experiments made with coloured discs bearing designs of different kinds.
The material needed for these discs is cardboard, covered with white paper
on one side, or the Bristol board used by artists. The discs on which the
designs are drawn should be made as large as the gramophone table will take
conveniently, so as to be viewed by a number of people at once. To
encourage readers who do not possess a gramophone, it may be pointed out
that a gramophone, is merely a convenience, and not indispensable for
turning the discs, which may be revolved on a sharpened pencil or any other
spindle with pointed ends.
The Vanishing Spirals (Fig. 137).--This design, if spun slowly in a
clockwise direction, gives one the impression that the lines all move in
towards the centre.
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