MAGNETISM DURING THE SEVENTEENTH CENTURY HH Ricker III

destroy the power of a lodestone. One was to place it near another more powerful stone, which
could
“...in a short time enchange its Poles; or being kept in undue position, that is, not lying on the
meridian or else with its poles inverted, it receives in longer time impair in activity.”
Browne’s chapter continues with a discussion of errors in magnetic history, medicine and magic.
He ends with a brief mention of the fundamental ideas of Gilbert’s magnetical philosophy that
motions of celestial bodies are due to magnetism. “Many other magnetisms may be pretended
and the like attractions through all the creatures of nature. Whether the same be verified in the
action of the Sun upon inferior bodies... whether the flux and reflux of the Sea be caused by any
Magnetism from the moon...might afford a large dispute”. Hence for Browne, Gilbert’s magnetic
philosophy remained merely an interesting unproved hypothesis. Browne also ignored many
other of Gilbert’s discoveries. Most significant is his complete failure to mention the experiments
which form the basis of Gilbert’s rudimentary field theory, and in particular Gilbert’s concept of
the orb of virtue. Apparently, the field theory concept was beyond the grasp of even the very best
educated English savants of the seventeenth century.
Galileo’s Researches in Magnetism
In continental Europe, Gilbert’s work was received with more enthusiasm. Kepler attempted to
incorporate it into his theory of the solar system. Galileo admired the experimental aspects and
performed his own researches. Vincenzio Viviani who liked to style himself as “the last disciple
of Galileo” describes some of Galileo’s magnetic experiments:
”towards the end of 1604 he had completed a long study of the properties of the
loadstones, and after many and varied experiments had found a sure way of arming any given
stone so as to make it sustain a weight of iron 80 to 100 times greater than could be supported by
the stone unarmed-a result which had not been reached by any investigator up to that time”. 6
It is believed that Galileo may have been performing experiments in magnetism prior to the
publication of On the Magnet. Professor Favaro of Padua, a biographer of Galileo, tells us that:
”our philosopher had been engaged on these studies for a considerable time, if not to a
date anterior to the issue of Gilbert’s book, certainly very soon after, when he verified all the
experiments of the English philosopher and instituted new ones of his own.” 6
It is certain that publication of Gilbert’s book stimulated him to active research in magnetism,
because we have letters written in the immediately following years which describe Galileo’s
experiment with loadstones. These experiments resulted in one sure demonstration of a repulsive
effect of magnetism, known as superposed magnetism. This is described in a letter written in
1608.
“I have also observed in this stone another admirable effect which I have not met with in
any other, namely, that the same pole repels or attracts the same piece of iron according to
distance. Thus, placing an iron ball on a smooth and level table, and quickly presenting the stone
at about a one finger’s distance, the ball moves away and can be chased about at pleasure. But