It is one which always succeeds, and is
productive of much amusement to the company.
Moisten slightly with water the rim of your plate, and in the center
paint with the yolk of the egg a sun with golden rays. By the aid of
this simple apparatus, you will be in a position to illustrate, so
clearly that a child can comprehend it, the double movement of the
earth, which revolves simultaneously round the sun and on its own axis.
All that you have to do is to place the empty half-shell of your egg
on the rim of the plate, and keeping this latter duly sloped, by a
slight movement of the wrist as may be needful, you will see the
eggshell begin to revolve rapidly on its own axis, at the same time
traveling round the plate. It is hardly necessary to remark that the
egg-shell will not travel uphill, and the plate must therefore be
gradually shifted round, as well as sloped, so that the shell may
always have an inch or two of descending plane before it.
The slight cohesion caused by the water which moistens the plate
counteracts the centrifugal force and so prevents the eggshell falling
off the edge of the plate.
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