134 Froceedings of Royal Society of Edinburgh. [sess. 
line, but I can see the blue colour nearly as far ; boundary indis- 
tinct and changeable, flashing. 
Potassium Spectrum. — I can see the extreme red line perfectly dis- 
tinct ; it appears a dark shade of yellow ; cannot, after many trials, 
see the extreme violet line, but can see difi“used colour nearly as far. 
Spectra of Na. Litli. and K. combined. The three lines at red 
end very beautiful. Na (589*3) powerful, full yellow; Li (670'5) 
also powerful and full, but rather darker; K (768) also coloured, 
but much darker. 
At Mr Hilgefs Manufactory, \bth August 1879. 
Moderate-sized spectroscope ; daylight, occasionally sunlight. 
Ked end and division confirm former notes. 
Paid more attention to the blue end. From the division it begins 
pale and watery like the yellow part, increasing in saturation to 
about G. Then it becomes darker, but the light being feeble, I do 
not see the shading so characteristically as on the yellow end. It 
appears to die gradually ofi*, losing light, till it disappears, and at 
the same time remaining full in colour, quite different from the 
light pale appearance near the division. 
Mr Hilger saw the two H lines very distinctly, but to me they 
were quite invisible ; all was in darkness where he put the pointer 
on them, and my colour did not extend so far. But I found by the 
scale that it went to about of the distance from G to H, i.e., 
very near to H. 
At Dr Hugginses Observatory, Ttdse Hill, Ibtli October 1879. 
The object of this visit was to observe the spectrum, with the aid 
of Dr and Mrs Huggins, and to determine carefully its appearance 
to me. This was done with a fine spectroscope, using either solar 
or daylight illumination, or electric sparks with different metals. 
I afterwards embodied the result in a coloured drawing, which I 
sent to Dr Huggins on the 18th October. (A chromo-lithograph 
imitation of this is given in the plate to my article in the Trans- 
actions of this Society, vol. xxxvii.) 
The division between the colours was confirmed at about the 
nitrogen line, which appears a dull, colourless hue, a sort of grey, 
not brilliantly white. 
