1868.] 



Solar Eclipse of 1868. 



119 



to look for faint ones, the positions of which I should estimate with re- 

 ference to those three. I should then direct the telescope at the brightest 

 part of the corona, taking very good care to prefer a part free from any 

 appearance of sierra, and if possible near the east or west points, so that 

 the slit might admit a vertical section. Assuming that the corona does 

 not emit tosochromatic light — if I may be allowed to coin a word to indi- 

 cate definite but unspecified colours, both in respect of number and tint 

 (or pitch) — of very distinct character, the spectrum of such a vertical slice 

 might indicate by its varying width that the light was not uniformly con- 

 stituted. Another point to be ascertained is whether all flames are con- 

 stituted alike. This would require a more or less rapid glance at the 

 spectra of several. I have spoken of " the three principal lines " because 

 J saw no others. I have, however, heard rumours of a greater number 

 having been seen by other observers, whether of equal brilliancy or not 

 I do not know ; but it inclines me to enforce the statement I have already 

 made of " three vivid lines — no more," as seen with a narrow slit. I had 

 no suspicion whatever of the presence of any but those three ; and as I 

 first saw them they were as sharp and bright as one could well wish to see. 

 Whether the prominence which I looked at was the same as those in which 

 more than three lines were seen I do not know. 



42. Lieut. Campbell 's Observations satisfactory in their result. 

 The determination of the polarization-plane of the corona is as satisfac- 

 tory as can be desired, and Lieut. Campbell's account is so clear that I have 

 little to say about it. It is to be regretted that he did not see the effect of 

 polarization all round at the same time, with a power low enough to in- 

 clude the whole of the phenomena ; but the view fortunately obtained with 

 the higher power remedies this in great measure by showing what would 

 have been seen at points 90° distant from that which he describes. 



43. Results with Hand Spectroscopes unknown. 

 With regard to the hand spectroscopes I have scarcely any report to 

 make. Lieut. Campbell had no opportunity. Capt. Haig has sent no re- 

 port. Neither have I heard anything of one of the two sent to sea. The 

 only record I have received is that of Capt. Rennoldson, of the ' Rangoon, 5 

 P. & O. Co.'s Steam Ship, which I enclose. He mentions having seen with 

 the spectroscope a prominence not seen by others with (I presume) ships' 

 glasses of greater power. This is difficult to understand, except on the 

 supposition that the light of the corona was weakened by dispersion, while 

 that of the flame was not, or not in so great a degree. Should it turn out 

 that the prominence he describes was a reality, it is barely possible that 

 the above explanation may be the true one ; in which case it suggests the 

 possibility of seeing the prominences with a heavy battery of prisms when 

 the sun is not eclipsed, especially if they are made of yellow glass ; nay, 

 even of seeing them, without the help of dispersion, through a medium 

 calculated to stop all light but that of the sodium flame. 



VOL. XVII. K 



