| Most early permanent magnets I have examined, both free-standing
and as part of magneto-electric machines, consist of several lamina of
thinner iron held together with rivets. This magnet in use at Kenyon College
at the left below is about 30 cm in length and normally has a keeper across
it; the keeper has a ring so that weights may be suspended from it to get
a measure of its strength. The iron must not have been very good, for I
often have to remagnetize the magnet before use. In the nineteenth century,
this was usually called a U-magnet.
The permanent magnet from Oberlin College at the right
below has four laminations, and is also painted the traditional red.
| These two permanent magnets are in the Garland Collection
of Classical Physics Apparatus at Vanderbilt University.
At the right is the Magnetic Battery made by Aimant Jamin
of France. This patented magnet assembly is made of 19 strips of steel,
each 5 cm wide. The bands used to hold the strips together are made of
a non-magnetic material, brass. This is listed at $45.00 in the 1888 catalogue
of Queen of Philadelphia
The U-magnet below has only one strip of steel,
and only the brass collar and hook betray its nineteenth century origin.
| During a visit to the physics lecture demonstration apparatus
collection at the University of Texas in Austin in January 2003, I saw
this small stand with the label of James W. Queen of Philadelphia stamped
on its upper surface. I was told that it was a holder for a bar magnet,
thus reproducing the geometer of the horizontal
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