58
ESSEX WORTHIES.
south. Most of these experiments were original with Gilbert, and are
indicated as such by him, by the placing of an asterisk opposite the
account of them in the margin of the book. These experiments and
aphorisms are continued in Chapter xxxiii., which deals mainly with
the swiftness of the magnetic motions, and he states that the speed of
the motion is proportional (inversely) to the distance. He also
showed that the magnetic forces between two distant magnets could
be conducted from one to the other by interposing a rod of iron ; the
magnetic virtue being transmitted through iron much better than
through air. At the end of this chapter he describes the method of
obtaining magnetic figures by sprinkling iron filings upon a card laid
over a magnet; and remarks on the movements of the tufts of filings
when the magnet beneath is moved. Chapter xxxv. contains a most
characteristic diatribe against certain earlier authors, Cardan, Peter
Peregrinus and John Taysnier, who had pretended that a perpetual
motion machine might be made by means of a magnet; and ends by
exclaiming : Would that the gods might send to perdition all such
false, misleading and crooked labours by which the minds of studious
men are warped!
Book III. is mainly occupied with the directive action of the
compass and of loadstones, and of the property of polarity—or
verticity—in general. Chapter i. describes further experiments with
the terrella made to illustrate observations made on the compass in
distant lands which had been communicated to Gilbert by Francis
Drake—experiments which fully confirmed his theories, and the
results of which are summed up by saying that all magnetic bodies
behave toward the globe of the earth precisely as other magnets
behave toward the terrella, the laws of their action being alike. In
the following chapters further experiments with loadstones and
needles are described, relating chiefly to the results of touching one
with the other. Amongst other matters which helped him to this
conclusion was his discovery that if a rod of iron is hammered whilst
lying in a north-and-south position it becomes magnetized by the
influence of the earth's magnetism. This observation is illustrated
by a quaint woodcut, which is reproduced on a smaller scale in
Fig. 3.
Books IV. and V. go into some geographical and astronomical
matters ; being intended chiefly as a contribution to the nautical
applications of his studies. He describes sundry instruments, one
of them, for ascertaining the variation of the compass in different