THE SUN'S SPOTS. 375 



that since 1706 similar red marginal protuberances have been 

 eight times described on the occasion of total or annular solar 

 eclipses. 18 On the 8th of July, 1842, when the apparently 

 larger disc of the Moon entirely covered the Sun, the Moon's 

 disc was observed to be surrounded not only by a whitish 

 light, 19 encircling it like a crown or luminous wreath, but 

 two or three protuberances were also seen, as if originating 

 at its margin, and were compared by some observers to 

 red jagged mountains, by others to reddened masses of ice, 

 and again by others to fixed indented red flames. Arago, 

 Laugier, and Mauvais at Perpignan, Petit at Montpelier, 

 Airy on the Superga, Schumacher at Vienna, and numerous 

 other astronomers, agreed perfectly in the main features of 

 the final results, notwithstanding the great differences in the 

 instruments they employed. The elevations did not always 

 appear simultaneously ; in some places they were even seen 

 by the naked eye. The estimates of the angles of altitude 

 certainly differed ; the most reliable is probably that of Petit, 

 the director of the observatory at Toulouse. He fixed it at 

 I' 45", which, if these phenomena were true sun-mountains, 

 would give an elevation of 40,000 geographical miles ; that 

 is to say, nearly seven times the Earth's diameter, which is 

 only 112th part of the diameter of the Sun. The conside- 

 ration of these phenomena has led to the very probable hypo- 

 thesis, that these red figures are emanations within the third 

 envelope, clouds, which are illuminated and coloured by the 



18 Arago, in the Annualre pour 1846, pp. 440-447. 



19 This is the white appearance which was also observed in 

 the solar eclipse of the 15th of May, 1836, and which the 

 great astronomer of Konigsberg very correctly described at 

 the time by observing " that although the Moon's disc en- 

 tirely covered the Sun, a luminous corona still encircled it, 

 which was a portion of the Sun's atmosphere." (Bessel, in 

 Schum. Astr. Nachr. No. 320. 



