THE APPROACHING TOTAL SOLAR ECLIPSE. 



29i 



quantity of light corresponding to the illumina- 

 tions of the air by the solar corona is much less 

 even than we should infer from the apparent 

 darkness of the moon's body at the time of total 

 eclipse. For we see that, of such light as does 

 seem to illuminate the moon's disk, a consider- 

 able portion, perhaps nearly all, must be earth- 

 light reflected from the moon's body. But, on 

 the other hand, we learn that the circumstances 

 under which a total eclipse is observed are very 

 unfavorable for the detection of faint light. We 

 see that a lustre ten or twelve times as bright as 

 that of a terrestrial surface, directly illuminated 

 by full moonlight, appears as actual blackness to 

 ordinary vision, and as the faintest possible light 

 to telescopic vision protected from the effects of 

 other light, at the time of total eclipse. It cer- 

 tainly does not seem likely, this being so, that as- 

 tronomers would be able either to ascertain pre- 

 cisely where the light of the solar corona begins 

 to be lost in the faint light due to the illumina- 

 tion of the air by that corona, or to trace on the 

 sky at the time of total eclipse the faint lustre 

 of the zodiacal light, barely discernible even at 

 night. 



We may, however, so far as the former point 

 is concerned, conclude that the whole of the co- 

 rona as seen at the time of mid-totality is solar. 

 A lustre so faint that even when added to ten or 

 twelve times the lustre of earth illuminated by a 

 full moon it is barely detectible during totality, 

 can surely not add appreciably to the extension 

 of the visible solar corona. 



Yet again, we can safely infer that any visi- 

 ble features in the crown of glory surrounding the 

 eclipsed sun must of necessity be solar phenome- 

 na. The light resulting from illumination by the 

 solar corona would be uniform, because rising 

 from a widely-extended region of luminous space ; 

 and though, if such light were brighter than we 

 have found it to be, it might occasionally show 

 the forms of various regions of the upper air in 

 which different conditions of moisture, tempera- 

 ture, and so forth, prevailed, yet even with bright 

 light this would be an exceptional phenomenon, 

 and with the exceedingly faint light we have been 

 considering it would be wholly impossible that 

 any such features could be brought into view. 



Unfortunately, while we thus learn that the 

 solar corona really has the extension which it 

 appears to have, that even when seen extending 

 farthest from the eclipsed sun it is not at all en- 

 larged by the atmospheric corona, we also per- 

 ceive that to recognize the fainter extension of 

 the corona beyond such distances as have hither- 



to been noted, will be a task of extreme difficulty. 

 In fact, when we remember that beyoud a certain 

 distance from the eclipsed sun we have a sky 

 partly illuminated by actual sunlight, even at the 

 time of central eclipse, we see that there must be 

 limits beyond which we cannot hope to trace the 

 corona. 



Nevertheless, I am inclined for my own part 

 to believe, or rather to hope, that the corona 

 may yet be traced much farther from the sun than 

 in any observations yet made, at least in any re- 

 garded as relating to the true corona. It may 

 even be possible to recognize the zodiacal light 

 itself during total solar eclipse. 



In the first place I would point out that ob- 

 servations have been made on certain occasions 

 which seem to indicate a much greater extension 

 of the visible corona than the appearances ordi- 

 narily seen and described. For instance, consider 

 the account of the corona as seen by General 

 Myer in 18G9: "To the unaided eye," he says, 

 " the eclipse presented, during the total obscu- 

 ration, a vision magnificent beyond description. 

 As a centre stood the full and intensely black 

 disk of the moon, surrounded by the aureola of a 

 soft bright light, through which shot out, as if 

 from the circumference of the moon, straight, 

 massive, silvery rays, seeming distinct and sep- 

 arate from each other, to a distance of two or three 

 diameters of the lunar disk, the whole spectacle 

 showing as upon a background of diffused rose- 

 colored light. This light was most intense, and 

 extended farthest at about the centre of the lower 

 limb. The silvery rays wera longest and most 

 prominent at four points of the circumference, 

 two upon the upper and two upon the lower por- 

 tion apparently equidistant from each other (and 

 at about thejunctions of the quadrants designated 

 as limbs), giving the spectacle a quadrilateral 

 shape. The angles of the quadrangle were about 

 opposite the northeastern, northwestern, south- 

 eastern, and southwestern points of the disk. A 

 banding of the rays, in some respects similar, has 

 been noted as seen at the total eclipse of July IS, 

 1860. There was no motion of the rays, which 

 appeared concentric " (that is, to radiate from 

 the same point, I suppose). 



Now, in this case the rays belonged certainly 

 to the solar corona. This was doubted by many 

 at the time, but the doubts belonged to the ex- 

 ploded theory that the corona, as a whole, is a 

 terrestrial phenomenon. We now not only know 

 that the corona belongs to the sun, but we know, 

 also, that it presents such radiations as General 

 Myer describes. They have been photographed, 



