This loadstone is under the care of certain astronomers, who, from
time to time, give it such positions as the monarch directs. They
spend the greatest part of their lives in observing the celestial
bodies, which they do by the assistance of glasses, far excelling
ours in goodness. For, although their largest telescopes do not
exceed three feet, they magnify much more than those of a hundred
with us, and show the stars with greater clearness. This advantage
has enabled them to extend their discoveries much further than our
astronomers in Europe; for they have made a catalogue of ten
thousand fixed stars, whereas the largest of ours do not contain
above one third part of that number. They have likewise discovered
two lesser stars, or satellites, which revolve about Mars; whereof
the innermost is distant from the centre of the primary planet
exactly three of his diameters, and the outermost, five; the former
revolves in the space of ten hours, and the latter in twenty-one
and a half; so that the squares of their periodical times are very
near in the same proportion with the cubes of their distance from
the centre of Mars; which evidently shows them to be governed by
the same law of gravitation that influences the other heavenly
bodies.
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