NOTES. CXXV 



Soleil." I have not thought it necessary to notice either the supposed moun- 

 tain ranges of 58,000 feet high which Schrb'ter imagined himself to have 

 measured on Mercury's disk, the existence of which was already doubted by 

 Kaiser (Sternenhimmell, 1850, 57) ; or Lemonnier's and Messier's state- 

 ment (Delambre, Hist, de 1'Astronomie au 18eme siecle, p. 222), of the 

 visibility of an atmosphere of Mercury during the planet's transit across the 

 Sun's disk ; or the suppositions of trains of clouds passing over the planet, 

 and transitory obscurations of its surface. During the transit of Mercury 

 which I observed in Peru on the 8th of November, 1802, I paid great atten- 

 tion to the sharpness of the outline of the planet during the emersion, but I 

 did not remark anything resembling an envelope. 



( M7 ) p. 348. " The part of the orbit of Venus in which the planet may 

 appear to us the brightest, so that it can be seen with the naked eye at noon, 

 is situated intermediately between the inferior conjunction and the greatest 

 digression, near to the latter, and nearly 40 degrees from the Sun, or from 

 the place of the inferior conjunction. On a mean or average, Venus appears 

 to us most bright and beautiful when distant 40 east or west of the Sun, 

 when her apparent diameter, which at the inferior conjunction may increase 

 to 66", is only about 40 ', and when the greatest breadth of the illuminated 

 portion scarcely measures 10". The nearness of the Earth then gives to the 

 narrow bow a light so intense, that, in the absence of the Sun, it even casts 

 shadows." (Littrow, Theorische Astronomic, 1834, Th. ii. S. 68.) Whether 

 Copernicus predicted the necessity of a future ' discovery of the phases of 

 Venus (as has been repeatedly stated, in Smith's Optics, Sect. 1050, and in 

 several other books) , has recently been shewn by Professor De Morgan's more 

 exact examination of the work De Revolutionibus, as it has come down to us, 

 to be extremely doubtful. (See the letter of Adams to the Rev. II. Main, dated 

 7th Sept. 1846, in Rep. of the Royal Astron. Soc. Vol. vii. No. 9, p. 142. 

 Compare also Kosmos, Bd. ii. S. 362; Eng. ed. p. 321.) 



( 558 ) p. 350. Delambre, Hist, de 1'Astr. au 18eme siecle, p. 256258. 

 Bianchini's result has been defended by Hussey and Flaugergues : Hansen, 

 whose authority stands justly so high, up to 1836 also regarded it as the 

 more probable. 



( 559 ) p. 350. Arago, on the remarkable Lilienthal observation of the 12th 

 of August, 1790, in the Annuaire for 1842, p. 539. " Ce quifavorise aussi 

 la probabilite de 1'existence d'une atmosphere qui enveloppe Venus, c'est le 

 resultat optique obtenu par 1'emploi d'une lunette prismatique. L'intensite 

 de la lurniere de l'interieur du croissant est seneiblement plus faible que celle 



VOL. III. g 



