308 Mr C. V. Burton, Experiments on Colour-Perception ; [Nov. 26, 
(5) Experiments on Colour-Perception ; and on a Photo-voltaic 
theory of Vision. By CHar.es V. Burton (B.Sc. London). 
I. Experiments on Colowr-Perception. 
Ir appears as yet to be an undecided question, whether or 
not the violet of the spectrum is physiologically redder than 
the blue. 
The present paper contains an account of some subjective 
experiments on colour-perception which were made at the 
Cavendish Laboratory, chiefly with the object of putting this 
question to the test. A spectroscope with two prisms was 
arranged so as to give a bright solar spectrum. On looking with 
one eye at a given part of the spectrum for about two minutes, 
the eye became fatigued, so that its sensitiveness to certain rays 
was diminished, and on turning to another part of the spectrum, 
a greater or smaller change of intensity and tint was perceptible, 
depending on the physiological relation of the colour now ob- 
served to that which had produced retinal fatigue. The ob- 
servation was assisted by using the untired eye as a standard 
for comparison. In place of looking at a selected portion of the 
solar spectrum, coloured glasses were usually employed to sift 
the light of the sun, the colours transmitted by them being of 
sufficient intensity to atfect the eye very powerfully. The 
fatiguing was continued for about two minutes at a time, and 
was constantly repeated during the observations, which were 
now made with a 4-prism spectroscope, so that only a limited 
range of colour was included in the field of view. A preliminary 
test having shown that the two eyes were very nearly alike “ 
in their perception of colours, and in their change of sensitiveness 
when fatigued for red, the fatigue was always subsequently 
produced in the right eye, and the left used for purposes of 
comparison. 
After looking at the sun through “red” glass (which transmits 
red, and orange, and a very little green), there was an apparent 
change of tint in the solar spectrum extending as far as the 
greenish-blue, the blue not being appreciably attected ; while on 
the other hand the violet looked very much bluer to the right 
eye and by contrast redder to the left. When the right eye 
was tired for green light, the yellow and yellowish-green appeared 
more orange, the green paler, and the greenish-blue bluer, while 
deep blue and violet were hardly affected. On tiring the right 
eye for blue and violet no change of appearance was observed 
in red, orange or yellow. Grass-green looked slightly paler and 
yeliowish, bluish-green and greenish-blue looked greener and 
paler, the blue duller and paler, and the violet distinctly redder. 
lt was often found that the impressions of the left eye were 
