CHROMOSPHERE AND SOLAR PROMINENCES. 387 



prominences : thus Captain Stannyan, in a report on the eclipse of 

 1706 observed by him at Berne, noticed that the emersion of the sun 

 was preceded by a blood-red streak of light, visible for six or seven sec- 

 onds upon the western limb. Halley and Louville saw the same thing 

 in 1715. Halley says that two or three seconds before the emersion a 

 long and very narrow streak of a dusky but strong red light seemed 

 to color the dark edge of the moon on the western edge where the 

 sun was about to reappear. Louville's account agrees substantially, 

 and he further describes the precautions he used to satisfy himself that 

 the phenomenon was no mere optical illusion, nor due to any imperfec- 

 tion of his telescope. 



In eclipses that followed that of 1733, the chromosphere and promi- 

 nences seem to have attracted but little attention, even if they were 

 observed at all. Something of the sort appears to have been noticed 

 by Ferrers in 1806, but the main interest of his observation lay in a 

 different direction. 



In July, 1842, a great eclipse occurred, and the shadow of the 

 moon described a wide belt running across Southern France, Northern 

 Italy, and a portion of Austria. The eclipse was carefully observed 

 by many of the most noted astronomers of the world, and so com* 

 pletely had previous observations of the kind been forgotten, that the 

 prominences, which appeared then with great brilliance, were regarded 

 with extreme surprise, and became objects of warm discussion, not 

 only as to their cause and location, but even as to their very existence. 

 Some thought them mountains upon the sun, some that they were so- 

 lar flames, and others, clouds floating in the sun's atmosphere. Oth- 

 ers referred them to the moon, and yet others claimed that they were 

 mere optical illusions. At the eclipse of 1851 (in Sweden and Nor- 

 way), similar observations were repeated, and, as a result of the dis- 

 cussions and comparison of observations which followed, astronomers 

 generally became satisfied that the prominences are real phenomena 

 of the solar atmosphere, in many respects analogous to our terrestrial 

 clouds ; and several came more or less confidently to the conclusion, 

 now known to be true {see Grant's " History of Physical Astronomy "), 

 that the sun is entirely surrounded with a continuous stratum of the 

 same substance. Many, however, remained unconvinced : Faye, for 

 instance, still asserted them to be mere optical illusions, or mirages. 



In the eclipse of 1860, photography was for the first time employed 

 on such an occasion with any thing like success. The results of Sec- 

 chi and De La Rue removed all remaining doubts as to the real exist- 

 ence and solar character of the objects in question, by exhibiting them 

 upon their plates gradually covered on one side and uncovered on the 

 other side of the sun by the outward progress of the moon. 



Secchi thus sums up his conclusions, which have been justified in 

 almost all their details by later observations ; they require few and 

 slight corrections : 



