That it was not brought from China to
Europe by Marco Polo, as some writers assert, is evident from the
circumstance that this traveller never mentions or alludes to it. The first
scientific account of the properties of the magnet, as applicable to the
mariner's compass, appears in a letter written by Peter Adsiger, in the
year 1269. This letter is preserved among the manuscripts of the university
of Leyden; extracts from it are given by Cavallo, in the second edition of
his Treatise on Magnetism. From these extracts it is evident that he was
acquainted with the attraction, repulsion, and polarity of the magnet, the
art of communicating those properties to iron, the variation of the
magnetic needle; and there are even some indications that he was acquainted
with the construction of the azimuth compass.
Next in importance and utility to the mariners' compass, in preparing the
way for the great discoveries by which the fifteenth century is
distinguished, maps and charts may be placed. For though, in general, they
were constructed on very imperfect and erroneous notions of the form of the
world, and the relative size and situation of different countries, yet
occasionally there appeared maps which corrected some long established
error, or supplied some new information; and even the errors of the maps,
in some cases, not improbably held out inducements or hopes, which would
not otherwise have been entertained and realized, as we have already
remarked, after D'Anville, that the greatest of Ptolemy's errors proved
eventually the efficient cause which led to the greatest discovery of the
moderns.
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