Prof. O. N. Rood on a New Theory of Light. 185 
before these tints make their appearance, or how long the tints 
are actually seen by the eye, is another matter, and would no 
doubt require an elaborate series of experiments, though it would 
seem probable that at least half of the time of the above given 
intervals passes before the subjective color makes its appearance. 
The table does not apply to the axial portion of the retina, 
which is almost always differently affected. ‘That the change in 
susceptibility in the retina is progressive outwards, is shown by 
the gradual expansion of the green ring; that it varies from 
sevond to second, is seen in the fluctuations of the outline of 
this ring. 
The occurrence and sequence of these subjective colors may 
easily be explained by supposing that during the interval of 
rest or shadow the action of the yellow rays diminishes more 
Tapidly than that of the red, the red more rapidly again than 
that of the blue. If this takes place as indicated by the curves 
below, it is easy to understand the production of the tints, for if 
4. the moment after the blue 
\ has been developed white 
\\ 
seen, sufficient time not 
having been allowed for their 
production, 
he same reasoning applies 
jo 
rar) 
r 
greater sensibility to such impressions of light, requires a some- 
What longer interval of rest before the reaction occurs. 
If the impression be too strong, that is, if the light be too 
Tight or the eye too long exposed to it, these peculiar effects 
‘re not observed, and during such short intervals of rest as ;'5 
or 7s of a second the white clouds seen through the dises suffer 
re ee In tint; but if a blackened disc ; 
elve Inches in diameter be cut as seen in 
Image of the sky, of a bluish-green tint. 
A ic it follows that an exposure of the 
oh white light lasting ,', of a second, : 
‘ai, eR in it for a considerably longer time the sensation of this 
AM, 
JOUR. SCL_SECOND SERIES, Vor. XXX, No. 89—SEPT., 1860. 
24 
