The axle on which the pointer revolves consists of a
piece of round wood, about the size of a lead-pencil, with a pin
driven in each end. A piece of tin, E, is cut V-shaped at each end
and bent up at the ends to form bearings for the pins. The silk
thread C is fastened to the wooden axle and is wrapped one or two
turns around it, so that when
[Illustration: The Hygrometer]
the thread is pulled the pointer will move on the scale. It will
be noticed that the thread B is not perfectly straight, but bends
toward D. For this reason a very small shrinkage of B, such as
occurs when the atmosphere is dry, will cause an increased
movement of C, which will be further increased in the movement of
the pointer. An instrument of this kind is very interesting and
costs nothing to make.
--Contributed by Reader, Denver.
** The Protection of a Spring Lock [72]
After shutting the front door and hearing the spring lock snap
into its socket, most people go off with a childlike faith in the
safety of their goods and chattels. But the cold fact is that
there is scarcely any locking device which affords less protection
than the ordinary spring lock.
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