THE SUN'S SPOTS. 71 



go, in putting forward this hypothesis, expresses the conjec- 

 ture that the intense blue color of the sky, which I have my- 

 self measured upon the loftiest part of the Cordilleras, though 

 with instruments which are certainly still very imperfect, 

 may afford a convenient opportunity for frequently observing 

 these mountain-like clouds in the outermost atmosphere of 

 the Sun.* 



When we consider the zone in which solar spots are most 

 commonly observed (it is only on the 8th of June and the 9th 

 of December, that the spots describe straight lines on the Sun's 

 disk, which at the same time are parallel with one another 

 and the Sun's equator, and not concave or convex), we are 

 struck by the fact that they have rarely been seen in the 



nous empechat d'admettre que des masses nuageuses de 25,000 a 

 30,000 lieues de long flottent dans 1'atmosphere du Soleil; que ces 

 masses, comme certains nuages de 1'atmosphere terrestre, ont des con- 

 tours arrctes, qu'elles atfectent, 93 et la, des formes tres tourmentees, 

 meme des forms en surplomb ; que la lumiere solaire (la photosphere) 

 les colore en rouge. Si cette troisieme enveloppe existe, elle donnera 

 peut.etre la clef de quelques-unes des grandes et deplorables anomalies 

 que 1'on remarque dans le cours des saisons " "On examining more 

 closely the grounds on which these rose-colored protuberances are com- 

 pared to clouds (of the third atmosphere), we do not find any principle 

 in physics which would oppose the assumption that masses of clouds 

 extending from 25,000 to 30,000 leagues, float in the Sun's atmosphere ; 

 that these masses, like some clouds in our terrestrial atmosphere, as- 

 sume contours exhibiting here and there much-involved forms, appear- 

 ing sometimes even sloping or inverted, as it were ; and that they are 

 colored red by the light of the Sun (the photosphere). If this third 

 atmosphere actually exist, it may, perhaps, tend to solve some of those 

 vast and deplorable anomalies which we observe in the course of the 

 seasons." Arago, in the Annuaire for 1846, p. 460, 467. 



* " Tout ce qui afiaiblira sensiblement 1'intensite eclairante de la 

 portion de 1'atmosphere terrestre quiparalt entourer et toucher le con- 

 tour circulaire du Soleil, pourra contribuer a rendre les preeminences 

 rougeatres visibles. II est done permis d'esperer qu'un astrouome ex- 

 erce, etabli au sommet d'une tres haute montagne, pourrait y observer 

 regulierement les nuages de la troisieme enveloppe solaire, situes, en ap- 

 parence, sur le contour de 1'astre ou un peu en dehors, determiner ce 

 qu'ils ont de permanent et de variable, noter les periodes de disparition 



et de reapparition " Whatever will perceptibly diminish the 



brilliant intensity of that portion of the terrestrial atmosphere which 

 appears to inclose and touch the circumference of the Sun, may con 

 tribute to render the rose-colored protuberances visible. We may 

 therefore, hope that an experienced astronomer may succeed, on the 

 summit of some high mountain, in making systematic and regular ob 

 servations of the clouds of the third solar envelope, which appear to be 

 situated on the margin of the Sun, or a little beyond to, and thus determ 

 ine the permanence or variability of their character, and note th 

 epochs of their disappearance and reappearance . . . ." Arago, Ibid. 

 p. 471. 



