201 



On the evening of 29tli January I succeeded in getting the 

 spectrum of a gas flame (common coal gas) turned down to a 

 minute point of blue flame, in juxtapt^sition with the spectrum 

 of the comet, when, to my surprise and gratification, I found 

 that the three comet lines coincided perfectly with the three 

 conspicuous lines shown in the gas spectrum; the principal 

 difference between the two spectra being, that the gas showed 

 a faint continuous spectrum through all the colours, whilst 

 that of the comet had perfectly dark spaces between the 

 lines, and, so far as I could discern, no colour. I cannot say, 

 however, that T might not have obtained a continuous 

 spectrum from the comet had I been able to grasp more of its 

 light. Such seemed to be suggested by the fact that the 

 lines were broadened out towards the violet end, gradually 

 fading away on that side, but were pretty sharp and decided 

 on the side next to the red. 



By a contrivance of my own, specially designed for 

 double star measurement, I was enabled to project a 

 dark-field " ghost " scale into the field of the spec- 

 troscope, and thereby got the relative positions of the lines from 

 the sodium line D. This line I obtained by sprinkling a little 

 salt in the gas flame. The mean of several observations gave 

 the following results (the readings of my scale being 

 reduced to that of Roscoe's frontispiece), for comparison : — The 

 line D being at 50, the comet lines stood at 59'3, 72*2, and 

 99 5. Eoscoe's carbon lines stand at 60, *7Q, and 100 ; also 

 another group at 123 to 128. This latter, however, I did not 

 detect. I think this agreement very close, and what little 

 difference there is may well be accounted for by a difference 

 of material of the prisms and the difiiculty of measuring. I 

 may mention that I took the precaution of scaling the 

 principal solar lines during the preceding afternoon for the 

 purpose of comparison. It was evidently chiefly, if not 

 entirely, the nucleus that gave the lines, as, on the briefest 

 stoppage of the driving clock, the lines instantly disappeared. 



I have contented myself with describing, as carefully as 

 possible, my observation, leaving to others more competent 

 than myself the interpretation of the record. I would venture 

 to remark, however, that my failure to detect continuity in 

 the spectrum would, as I read it, indicate that the self 

 luminosity of the comet must greatly overpower whatever 

 sunlight it reflects. 



