222 On White Lines in the Solar Spectrum. [Feb. 26, 



Note for diagram. In course of studying the solar spectrum for atmo- 

 spheric lines, with an excellent 3-prism (new) spectroscope belonging to 

 the Royal Society, I gradually extended my search, begun at the red end, 

 until on arrival at the region about b my attention was attracted by the 

 fact that K 1657*1 by no means appeared as the strong line depicted in 

 Kirchhoff's map, Plate II. On examining this region carefully, I was 

 surprised to find the colourless lines shown in the diagram ; these lines, 

 from want of a more appropriate name, I shall call white lines (or spaces) ; 

 they cannot absolutely be described as bright lines, yet they closely re- 

 semble threads of white floss silk held in the light. The spectroscope in 

 use, with the most convenient highest-power eyepiece, presents images 

 of about two thirds to seven ninths of those drawn in the diagram ; the 

 former are exaggerated by reckoning to agree with Kirchhoff's millimetre 

 scale ; it will therefore be readily understood that the white lines do not 

 present striking objects in the spectroscope, especially about the time of 

 sunset, when I happened first to notice them ; they are best seen about 

 noon, when their resemblance to threads of white floss silk is very close ; 

 but once seen, the lines in question can always be readily detected. So 

 far as my instrumental means permit, the wider line extends between 

 K 1657*1 and K 1658-3 ; more accurately speaking, it falls short of the 

 latter and rather underlies the former ; the narrower white line is under- 

 neath K 1650-3, sensibly more of the former appearing beyond the edge 

 towards violet of the latter, which presents the quaint look of a black 

 line on a white surface enclosed in a green band. These are the only 

 white lines in the spectrum from extreme red to E ; they are not bright 

 (or reversed lines), so far as I have had opportunity to judge. Were they 

 bright lines, the question would arise, why these alone should be reversed 

 at 6700 feet above sea. Like the black lines the white lines grow dim 

 and disappear with the slit opened wide. As seen here, K 1657'! is sen- 

 sibly weaker than K 1667'4, whereas Kirchhofl: assigns 5 6 to the former 

 and only 3 a to the latter. 



A Photograph of the Moon, sent by the Rev. Dr. Robinson, E.R.S., 

 taken with the Great Melbourne Equatorial, was exhibited ; also a 

 lithograph of the Nebula in Argo, made from eye-observations with the 

 same instrument. 



