The bolt in making one revolution will descend a
distance equal to the distance between the threads.
The device is used by placing the object whose thickness is to be
measured on the base under the bolt, and screwing the bolt down
until its end just touches the object, then removing the object,
and screwing the bolt down until its end just touches the base,
carefully noting while doing so the distance that the end of the
wire moves over the scale. The part of a rotation of the bolt, or
the number of rotations with any additional parts of a rotation
added, divided by the number of threads to the inch, will be the
thickness of the object. Quite accurate measurements may be made
with this instrument, says the Scientific American, and in the
absence of the expensive micrometer, it serves a very useful
purpose.
** Another Electric Lamp Experiment [131]
Break a portion of the end off from a 16-cp. globe that has been
thrown away as useless. Shake the globe until all the filament is
broken away, leaving only the ends of the platinum wire exposed.
Screw the globe into a socket that sets upright and fill it with
salt water.
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