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 dis- 

 coveries which scarcely comprised two years, and in which 

 the great and undying name of the Florentine shines pre- 

 eminent, 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 De- 

 cember, 1610, in accordance with a practice already alluded 

 to, he concealed this important discovery in an ana- 

 gram, 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, notwith- 

 standing 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 exist- 

 ence of these phases ; and, we find, that he discusses circum- 

 stantially, 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 dis- 

 sensions 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 

 Herschel, in his Astronomy, . 334, speaks of the experiments with 

 Drummond's light projected on the sun's disk. 



t 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 Nelli, Vita, vol. i. pp. 213-215. 



