480 The approaching Total Solar Eclipse. [Oct., 



The main object of the astronomers of this and other countries 

 will be to determine the nature of the corona. For this purpose, 

 each of the English expeditions is to be divided into four parties. 

 First, there will be the spectroscopists ; secondly, the polariscopists ; 

 thirdly, the photographers ; lastly, there are the general observers, 

 who in our opinion are very far from forming the least important 

 portion of the expedition. 



The spectroscopic evidence obtained during the Indian and 

 American eclipses is contradictory and unsatisfactory. Let it be 

 remarked in passing, however, that it is not altogether so contra- 

 dictory as has been asserted. The American observers appear to 

 have been misled into the supposition that Major Tennant saw the 

 ordinary solar spectrum — that is, that the Fraiinhofer lines could 

 be seen in the spectrum of the corona. And indeed in Prof. Roscoe's 

 treatise ' On Spectrum Analysis,' it is stated that Major Tennant 

 saw the ordinary solar spectrum, whereas " Professor Pickering, on 

 the other hand, saw only a continuous spectrum." But Major 

 Tennant's account expressly asserts that the spectrum he saw was 

 continuous. He says, " What I saw " (the italics are his) " was 

 undoubtedly a continuous spectrum, and I saw no lines. There 

 may have been dark lines, of course, but with so faint a spectrum 

 and the jaws of the slit wide apart, they might escape notice." 

 Thus the continuous spectrum seen by some of the American 

 observers is in perfect accordance with Major Tennant's observation. 

 Indeed the mistake is rather fortunate than otherwise, because it 

 led the American observers to search specially for dark lines such 

 as they supposed Tennant to have seen ; and, therefore, their failure 

 to recognize any may be regarded as all but decisive of the matter. 



Where Major Tennant's observations are not accordant with 

 those made by the American observers, these latter observations are 

 themselves wanting in accordance. For Professor Young saw three 

 bright lines in the coronal spectrum, and Professor Harkness saw 

 one bright line; whereas Professor Pickering, like Major Tennant 

 in 1868, saw only a continuous spectrum. This discrepancy will, 

 we may fairly trust, be cleared up during the approaching eclipse. 

 It may perhaps be found that different parts of the corona give 

 different spectra. It may be noticed, however, that the bright line 

 seen by Harkness and the bright lines seen by Young were delicate 

 objects, and would almost certainly have escaped notice had these 

 observers used a much narrower or a much wider slit than they 

 actually employed. Professor Harkness failed to see the line till 

 he had slightly opened the slit ; but he would probably have lost 

 it equally had he widened the slit too much.* May not Major 



* The total quantity of light from the bright lines would be increased by widen- 

 ing the slit; but the intrinsic brilliancy of the broadened bands would be no greater 

 than before. On the other hand, the intrinsic brilliancy of the continuous back- 

 ground would be increased by the change. 



