The apparatus is then short-circuited, yet
there is no current in the instrument until a lighted match, or,
better still, the flame of an alcohol lamp is placed at one end
only.
Best results are obtained by putting ice or cold water on one side
and a flame on the other. The experimenter may also place the
whole apparatus under sink faucets with the hot water turned on at
one terminal and the cold water at the other. The greater the
difference of temperature in the two terminals, the more current
will be obtained.
Very interesting experiments may thus be performed, and these may
lead to the solving of the great thermoelectric problem.
** How to Make a Hygrometer [140]
Mount a wire on a board which is used for a base and should be 3/8
by 4 by 8 in., as shown in the sketch. A piece of catgut--a string
used on a violin will do--is suspended from the bent end of the
wire. A hand or pointer is cut from a piece of tin and secured to
the catgut string about 1/2 in. from the base. A small piece of
wood and some glue will fasten the pointer to the string. The
scale is
[Illustration: Simple Hygrometer]
marked on a piece of cardboard, which is fastened to the base and
protected with a piece of glass.
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