Baldwin explores the arguments of the anti-Copernicans that
sought to bolster their astronomical claims by appealing to the science of
magnetism that was also being used by the heliocentrists.
Kepler and Galileo both applied magnetism to their astronomical
physics as being agents that explained aspects of planetary motions. The
elliptical orbits of the planets that had been observed were said to be because
of the magnetic force. The constancy of the polar tilt of the Earth was due to
the magnetic force. These were things that could be seen using a spherical
lodestone as Gilbert did in his original work, and I can understand why that
would hold so much weight because we as people like being able to see something
to tell whether or not it is true. The use of an analogous system is powerful
in that way for teaching physics.
Cabeo was a Jesuit that took issue with the Copernican
notion of a heliocentric system, and he wrote a full treatise on magnetism. He
conceded that the whole Earth participated in magnetic virtue, but he did not
hold that the Earth was a big magnet itself. He felt this way because of how
weak the magnetic field was measured to be, and that if the Earth were such a
large magnet, the minor (by comparison) lodestones that were used to study
magnetism would have negligible effect on compass needles. Cabeo felt that the
role of the magnetic force of the whole Earth was that of an emergency force used to correct the rotation
and position of the heavens should they become dislodged.
Continuing to read through the works that Baldwin has
collected, it is apparent how the choices of the Church played heavily into the
usage of the magnetic force in astronomy. In the end, the subject was dropped
altogether as having impact on astronomy, but it seems to have essentially
fizzled out as scientists went on to study other phenomena that were unfettered
by ecclesiastical debates.
Tying this in with DiSessa, I can see a pitfall that
students would fall into that is illustrated by the Copernicans and anti-Copernicans.
The magnetic force was a hot topic item when Gilbert penned his work on it. The
usage of it in the astronomies to describe the different motions is fair
evidence to that fact. We know now today that things are the way they are due
to gravitational attraction and the physics governing bodies in such a system
as our Solar system, but they were unaware of that. Students, upon learning a
new concept to build upon and advance the p-prims that they have, will possibly
be anxious to make use of that knowledge in new ways that they find. I feel
that it is important to make sure that they understand the when for making use
of this new knowledge just as much as the how.
Martha Baldwin, "Magnetism and the anti-Copernican polemic," Journal for the History of Astronomy, Vol. 16, pages 155-174 (1985)
