COSMOS, VOL. II - World eBook Library

708 COSMOS.
descent lime-ball appears inky black when thrown on the sun's
disk, we cannot wonder that Galileo, who undoubtedly, first
described the great solar
faculce, should have regarded the
light of the nucleus of the sun's spots as more intense than
that of the full moon, or the atmosphere near the sun's disk.*
Fanciful conjectures regarding the many envelopes of air,
clouds, and light, which surround the black earth-like nucleus
of the sun, may be found, in the writings of Cardinal Nicholas
of Cusa, as early as the middle of the fifteenth century, f
To close our consideration of the cycle of remarkable discoveries
which scarcely comprised two years, and in which
the great and undying name of the Florentine shines preeminent,
it still remains for us to notice the observation of
the phases of Venus. In February 1610, Galileo observed the
cresoentic form of this planet, and, on the llth of December,
1610, in accordance with a practice already alluded
to, he concealed this important discovery in an anagram,
of which Kepler makes mention in the preface to his
Dioptrica. "We learn also, from a letter of his to Benedetto
Castelli (30th of December, 1610), that he believed, notwithstanding
the low magnifying power of his telescope, that he
could recognise changes in the illumined disk of Mars. The
discovery of the moon-like or crescent shape of Venus was the
triumph of the Copernican system. The founder of that sys-
tem could scarcely fail to recognise the necessity of the existence
of these phases ; and, we find, that he discusses circumstantially,
in the tenth chapter of his first book, the doubts which
the more modern adherents of the Platonic opinions advance
against the Ptolemaic system on account of these phases.
But, in the development of his own system, he does not speak
expressly of the phases of Venus, as is stated by Thomas
Smith in his Optics.
The enlargement of cosmical knowledge, whose description
cannot, unhappily, be wholly separated from unpleasant dissensions
regarding the right of priority
to discoveries, excited,
*
See some ingenious and interesting considerations on this subject
by Arago, in the Annuaire pour Van 1842, pp. 481-488. Sir John
334, speaks of the experiments with
Herschel, in his Astronomy, .
Drummond's light projected on the sun's disk.
f Giordano Bruno und Nic. von Cusa vergliclien, von J. Clemens,
1847, s. 101. On the phases of Venus, see Galilei, Opere, t. ii. p. 53,
and Kelli, Vita, vol. i. pp. 213-215.