By Pasquale Stroppa
This instrument is very easily constructed. In making It the following
materials are required:
A pocket compass, two bar magnets, and
Take a board about three feet in length
by four inches in width and one-half inch
thick. At the end of the board, about
one Inch from the edge, bore a hole so
that the compass will fit tightly therein.
The compass must at least penetrate the
board so that the glass disk will be a
little above the hoard and the needle of
the compass will he about on the level of
the surface of the board.
Now begin from the compass and measure one inch spaces to about thirty in
number and mark the lines beginning
from the compass needle one, two, three,
four, and so on.
When this has been done, place the
board on a table. The compass needle
will then come to rest pointing to the
magnetic north and south. Turn the
hoard so that the needle will be at right
angles to the longitudinal axis of the
board. The compass needle must be right
over the north and south poles thereof,
and the north point of the needle must
point to 0.
The instrument is now ready for use.
Take one of the magnet bars and place
it on the board, so that either one of
its poles points to the compass needle.
Now move the bar magnet toward the
compass needle until the needle shows deflection. This may be as much as ten degrees on the compass dial with a distance
of twenty-five inches for the pole of the
magnet under trial. Remove this magnet,
and place the other magnet at the same
distance. The magnetic needle may be deflected twenty degrees at the same distance of twenty-five inches. This shows
that the bar magnet tested last was
stronger than the first one, or ten degrees
stronger, taken arbitrarily.
An electromagnet can also be tested in
the same manner. This instrument can
be used to test any of two bar magnets
so as to determine which of them is the
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