THE SUN s spois. 65 



green stained glasses in solar observations, wliich had l^een 

 proposed seventy years earlier by Apian (Bienewitz), in the 

 AstronoTnicum Coisareum, and had also been long in use 

 among Belgian pilots.^ The neglect of this precaution con- 

 tributed 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 observa- 

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

 with in the writings of the great Dominique Cassini,t and 

 belongs probably to about the year 1671. According to his 

 views, the solar disk which we see is "an ocean of light sur- 

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

 movements {up-ivellings) which occur in this luminous en- 

 velope enable us from time to time to see the mountain sum- 

 mits of the non-luminous body of the Sun. These constitute 

 the black nuclei in the center of the Sun's spots." The ash- 

 colored penumbraB surrounding these nuclei had not then been 

 explained. 



between 1618 and 1626. This period includes the years for which 

 Scheiner pubhshed his own observations at Rome in his Rosa Ursina. 

 The Canon Tarde believes those appearances to be the transits of small 

 planets, because "I'ceil du monde ne pent avoir des ophthalmies," " the 

 eye of the universe can not experience ophthalmia." It must justly 

 excite surprise that the meritoi'ious observer, Gascoigne (see Cosmos, 

 vol. iii., p. 61), should, twenty years after Tarde's notice of the Bor- 

 bonic satellites, still have ascribed the Sun's spots to a conjunction of 

 numerous planetary bodies revolving I'ound the Sun in close proximity 

 to it and in almost intersecting orbits. Several of these bodies, placed, 

 as it were, one over another, were snpposed to occasion the black shad 

 ows. (Philos. Transact, vol. xxvii., 1710-1712, p. 282-290, from a let- 

 ter of "William Crabtree, August, 1640.) 



* Arago, Sur les vioyens d' Observer les taches Solaires, in the Annii- 

 aire pour Van 1842, p. 476-479 ; Delambre, Hist, de V Astronomie du 

 Moyen Age, p. 394 ; and his Hist, de V Astronomie Moderne, tom. i., p. 

 681. 



t Mimoires pour servir a V Histoire des Sciences, par M. le Comte de 

 Cassini, 1810, p. 242 ; Delambre, Hist, de VAstr. Mod., tom. iii., p. 694. 

 Although Cassini in 1671, and La Hire in 1700, had declared the Sun'a 

 body to be dark, otherwise trustworthy and valuable text-books on as- 

 tronomy still continue to ascribe the first idea of this hypothesis to the 

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

 torn, iii., § 3240, as in the first edition of 1764, tom. ii., § 2515, 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 com- 

 mnnement (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 and 1774, conceived the fitw 

 correct view of a funnel-shaped opening in the photosphere. 



