. 
246 E. L. Nichols—Color Impressions upon the Retina. 
the light and with the condition of the observer’s eye. The 
variations due to the change of sensitiveness of the eye were so 
marked and so rapid that any attempt to compare different por- 
tions of an extended series of measurements o be aban 
d 
through the spectrum, taking a single measurement in each 
region, it was found possible to obtain series of readings during 
the course of which the eye had not appreciably varied. 
The method of observation was very simple. The axle 
upon which the disk revolved was connected by an endless. 
band with a fly wheel of weight sufficient to insure the neces- 
sary uniformity of motion. is fly wheel was turned by the 
observer, who increased its speed, watching the spectral region 
under inspection, until the appearance of the above mentioned 
shadow indicated the transition from interrupted to continuous 
Series A, 
Revolutions Interval between Duration of 
Spectral region. per minute. exposures of retina. 
7420 (red) 136 0°1074 seconds. — 0°00293 seconds. 
6463 (orange) 150 00961 “« 000266“ 
6025 (yellow) 171 00850 =“ 0-00232  “ 
5415 (green) 140 071044“ 000285 =“ 
4784 (blue) | = 130 C1155: 4: 000306“ 
4382 (violet) 88 O166e * 000452“ 
Series B. 
[Spectrum brighter than in Series A.] 
Revolutions Interval between Duration of 
Spectral region. per minute. exposures of retina. expo 
7420 (red) . 154 0°0949 seconds, —_ 0°00259 seconds. 
6463 (orange) 186 a‘ be 0024. * 4 
6025 (yellow) 260 00562 “ 0°00153 _* 
5415 (green) 180 oogi2 . + 0.00221 “ 
4784 (blue) - 144 O1015 . « 000277.“ 
4382 (violet) 108 01355 * 000369 =“ 
i 
4 
4 
4 
um 
. 2 = 
