368 COSMOS. 



stained glasses in solar observations, which had been proposed 

 seventy years earlier by Apian (Bienewitz), in the Astrono- 

 micum Ccesareum, and had also been long in use among 

 Belgian pilots. 10 The neglect of this precaution contributed 

 much to Galileo's blindness. 



As far as I am aware, the most definite expression of the 

 necessity for assuming the existence of a dark solar sphere, 

 surrounded by a photosphere, grounded upon direct obser- 

 vation after the discovery of the Sun's spots, is first to be 

 met with in the writings of the great Dominique Cassini," 

 and belongs probably to about the year 1671. According to 

 his views, the solar disc which we see is "an ocean of light 

 surrounding the solid and dark nucleus of the Sun ; the violent 

 movements (up-wellings) which occur in this luminous enve- 



Transact, vol. xxvii. 1710-1712, pp. 282-290, from a letter 

 of William Crabtree, August, 1640.) 



10 Arago, Sur les moyens d 'observer les taches solaires, in 

 the Annuaire pour Ian 1842, pp. 476-479. Delambre, 

 Hist, de VAstronomie du moyen age, p. 394; and his Hist, 

 de I'Astronomie moderne, torn. i. p. 681. 



u Memoires pour servir d VHistoire des Sciences, par M. le 

 Comte de Cassini, 1810, p. 242 ; Delambre, Hist, de I'Astr. 

 mod. torn. iii. p. 694. Although Cassini in 1671, and La 

 Hire in 1700, had declared the Sun's body to be dark, other- 

 wise trustworthy and valuable text-books on astronomy still 

 continue to ascribe the first idea of this hypothesis to the 

 meritorious Lalande. Lalande, in the edition of 1792, of his 

 Astronomic, torn. iii. 3240, as in the first edition of 1764, 

 torn. ii. 2,515, merely adopts the older view of La Hire, 

 according to which " les taches sont les eminences de la' 

 masse solide et opaque du Soleil, recouverte communement 

 (en entier) par le fluide igne;" " the spots are the elevations 

 of the solid and opaque mass of the Sun, covered by an 

 igneous fluid." Alexander Wilson, between the years 1769 

 und 1774, conceived the first correct view oi a iunuel-shaped 

 opening in the photosphere. 



