SPECTROSCOPIC OBSERVATIONS. 79 



corona line (" 1474 K ") is interesting, as it entirely confirms the 

 wave length obtained by Mr. Fowler for this line. The mean 

 of measures of the line on Plates Nos. 3 and 7, gives a position 

 about 14 units more refrangible than the value (A, 5317) which 

 has for so long been accepted as the true value. 



Six of the ten photographs of the prismatic camera series are 

 reproduced in the accompanying plates, the series number and 

 time of exposure being given under each spectrum. They are 

 enlarged from the original negatives about twice, and show the 

 principal features very well. The hydrogen lines are well seen 

 in Nos. 3 and 7, the ultra-violet members of the series to the 

 left hand of the pair of strong lines H and K, which will be 

 easily recognised on each spectrum near the middle of the plate. 

 The first strong line to the left of K is the hydrogen line f, 

 and the others follow at regularly decreasing intervals, and 

 diminishing intensity. It will be observed, however, that there 

 is a strong line near the end of the series (between p and o-), 

 and a close pair of equally strong and long lines between i 

 and #, which appear to spoil the harmony of the series : these 

 are the three titanium lines referred to above. 



With a view to making a direct comparison between the 

 flash spectrum and the Fraiinhofer spectrum, I have prepared 

 a plate in which these two spectra are placed side by side. By 

 photographing a narrow longitudinal strip of No. 1 and No. 3 

 spectra with the interposition of a cylindrical lens, the short 

 sections of the curved arcs are spread out into straight lines, 

 which give to the spectra the conventional appearance, and aid 

 in the comparison. 



The Fraiinhofer lines in No. 1, although much weaker than 

 in the ordinary solar spectrum, are nevertheless very clearly 

 defined in the original negative, and a comparison can be made 

 with very great exactness. From a mere inspection of the 

 plate in which these spectra are compared, it will be noticed 

 that whilst some of the strong lines in the flash are reversals of 

 strong Fraiinhofer lines, a large number of conspicuous flash 

 lines appear to have no corresponding dark lines. The calcium 

 lines H and K, and many iron lines, are instances of the former, 

 whilst the titanium and ultra-violet hydrogen lines may be 

 taken to represent the latter. Many of the strong flash 

 spectrum lines are, however, in reality represented by dark 

 lines in the Fraiinhofer spectrum, only the relative intensities 

 are very different in the two spectra. Thus the titanium lines 

 referred to above have their counterpart in the Fraiinhofer 

 spectrum, appearing in the ordinary solar spectrum as fine 

 lines, which are, however, too weak to show at all in the cusp 

 spectrum. 



It would be out of place in this report to describe in any 

 further detail the results which follow from a study of these 



