1892 - 93 .] Dr William Pole on Colour-Blindness, 
133 
AG. 
Notes of my own Observations on the Appearance of 
THE Spectrum, 1879. 
At Prof. Lockyer'^s Laboratory, South Kensington, July 1879. 
Observed an air spectrum, made by an electric spark, Avhicb gave 
a discontinuous spectrum of a great many lines. 
All the left hand ones appeared yellow ; all the right hand ones 
appeared blue. The division between the colours was well marked 
by a broad line, which appeared to me white. [This, I was told, 
was a green double line of nitrogen, lo.l. 500‘5 and 500‘2.] This 
had a narrower line on each side of it, pretty close ; the left hand one 
appearing yellow, the right hand one blue. 
At the same place, Wth August 1879. 
Observed the spectrum of white light from the sky ; no sun. 
At the red end, Mr Miller and I could just distinguish line B, 
but nothing beyond. 
The yellow colour, going towards the red end, begins to darken 
about half-way between D and C, and the darkening increases till 
the illumination disappears, just like the shading of a round column 
in an engraving, the yellow colour being always maintained. 
Going from the maximum yellow towards the right hand, the 
colour begins to pale off shortly before E, and gets paler, more watery, 
up to the division of the colours. This is quite a different effect from 
the shading at the red end ; it is clearly caused by the admixture 
of white light, and the consequent reduction of intensity of colour. 
Erom near E to half-way between C and D the colour is very 
brilliant, and seems tolerably uniform. 
The division of the yellow from the blue appears about half-way 
between h and F, or may be nearer h, say &JF but it is indistinct 
and variable, flashing sometimes bluer, sometimes yellower. 
From the division, going towards the blue end there is first the 
same paleness, the colour gradually augmenting to about G, where 
it seems full. Beyond this, uncertain j the colour seems full and 
deep, but somewhat dark ; vision near end indistinct, flashing ; 
cannot positively trace the shading. As to the extremity visible, 
Mr Miller can see just as far as the line /q 410T. I cannot see the 
