1894.] The Total Solar Eclipse of 16th April, 1893. 23 



The Prominence Spectrum. 



This list gives the wave-lengths of all the lines in one prominence 

 from each photograph. The second prominence on the two-prism 

 spectroscope plate is of a similar character to the one given, bui 

 contains fewer lines. 



The intensities of the lines are given approximately by the numbers 

 from 1 to 6. 



The most interesting feature of this spectrum is the extended 

 hydrogen series. There seems no reason to doubt that the lines at 

 wave-lengths 3692'5, 3687, 3682, 3678, 3675, 3672, 3669'5, and 

 3667 are members of it. 



M. Deslandres has obtained a photograph showing five hydrogen 

 lines beyond the one at wave-length 3699 ; this photograph carries the 

 series three lines further. The line at 3680 is the iron line, whose 

 wave-length is given by Cornu as 3680'3, and by Hartley as 3679'5. 

 The new notation for the hydrogen series has been used as con- 

 venient. HJ3 is F, [7 the line near G, and so on, consecutively. 



The Corona Spectrum. 



This is the final adopted list, as described above. It is almost 

 impossible to estimate the intensity of these feeble lines by eye, so 

 no attempt has been made to do so ; but in the column headed 

 "intensity" is placed the number of occurrences of the line in the 

 two photographs, the maximum number being four, viz., on each 

 side of both photographs. 



Opposite each line in the table is placed the corresponding line that 

 has been noted in previous eclipses. For a complete list of the ob- 

 served corona spectrum, see Dr. Schuster's report on the eclipse of 

 1886 ('Phil. Trans.,' vol. 180 A, p. 335). 



It will be observed that the 1474 K, or so-called corona line, is 

 placed in the prominence and not in the corona spectrum. This 

 line is shown very faintly on the extreme limit of one photograph, in 

 which it certainly appears to belong to the prominence. It is true 

 that it extends into the corona, but at the same time it also extends 

 in the opposite direction, over the dark body of the moon. Its appear- 

 ance is somewhat similar to that of the strong hydrogen lines, whose 

 apparent extension into the corona spectrum is probably due to atmo- 

 spheric haze. 



This region of the spectrum has never been specially photographed 

 with the slit spectroscope during an eclipse, and I think a serious! 

 attack on it should most certainly be made at the first opportunity, by 

 using plates which can now be prepared, which are specially sensitive 1 

 to this region of the spectrum. 





