334 
CAPTAIIn^ L. DARWIJf, DB. A. SCHUSTER, AND MR. E. W. ]\IAUNDER 
Distance from H. 
CoroiiJi line. 
Calcium line. 
■b9-io 
•5810 
•5920 
•6810 
•5950 
•5752 
•5930 
•5780 
•5930 
•5790 
•5920 
*■5804 
•5930 
-*■5816 
•5930 
*•5804 
5902 
•5810 
•5910 
•6824 
•5930 
•5822 
*•5904 
Mean . ^5923 
Mean . ■5802 
Keduced to wave-lengths, the difference is 6'4, and, taking the wave-length of the 
calcium line as 4226‘4, I arrive at the adopted wave-length 4232‘8. 
The plate taken with Spectroscope I. was more difficult to reduce. When the G 
absorption and the strong corona line had been recognised, the distances of the other 
lines were measured, and the corresponding wave-lengths found by help of the 
reference spectrum. All measurements of this plate were taken by Mr. Stanton, as 
my eyes could no longer stand the strain. The measurements are very difficult, as the 
band which has left a mark on the plate is exceedingly narrow, and it is sometimes 
impossible to distinguish accidental spots from real lines. Mr. Stanton has found a 
number of apparent absorption lines in the spectrum. Most of these, agree with 
strong Frauiihofer lines, and this justifies the belief that his measurements are sub¬ 
stantially correct as giving the positions of certain markings on the plates ; but it is 
cjuice possible that specks of dust or other accidental marks have occasionally been 
taken for corona hires. 
The following Table gives a list of the lines Avhich have been measured on the two 
plates. For reference, the corona lines observed in 1882 and 1883 have been added. 
A query is attached to those wave-lengths taken in 1883 which have not been included 
in Captain Abney’s final list. The lines which are printed in thicker type are those 
i have measured repeatedly, and about which I can speak therefore with greater 
confidence; but ail lines given have been measured at least twice. In the column 
headed intensity-—(6) represents the highest intensity, and (l) the lowest. The 
intensities refer to the appearance of the lines in the centre of the spectrum, that is, on 
the prominence line. The numbers given are, of course, very approximate only, as 
the judgment about intensities much depends on the fatigue of the eye and other 
circumstances. Down to intensity (3) the lines are easily visible ; (2) means more 
difficult to see, but not doubtful; the lines marked (l) are doubtful. 
