184 Prof. O. N. Rood on a New Theory of Light. 
Upon increasing the rate of revolution, the bluish- 3, 
green spot expanded into an irregularly shaped 
ring, and continued to expand, filling the field, till 
the rate had become as high as 15 rotations per 
second, when often the field for an instant became 
of a greenish tint which was succeeded by a bluish 
tint; upon increasing the speed this also vanished. 
Still higher rates cease to produce any of these pe- | puRPrE 
culiar effects on the eye. SERS 
Upon slowly reducing the rate to 9 revolutions per second, 
the green spot contracted in dimensions, and assumed a w 
tint, while the field often became at the same time tinted deep 
crimson. With a rate still lower, the appearance of the field 1s 
variable and the tints flickering; it assumes sometimes a purple, 
a yellow, or a yellowish green tint. : 
This experiment I repeated a great number of times, with the 
same general result, and though it sometimes happened that the 
eye became insensible to these colors, from repetition, momentary 
rest in darkness restored this power for a short time. ‘Thus it 
occurred that the tints were sometimes seen with great distinct 
ness, While at others they could hardly be distinguished. 
on a dark cloudy day to produce these effects it was found 
necessary to increase the width of the slits to 20°; from whence 
it was manifest that lack of intensity in the light might be made 
up by its longer duration. 
It would appear then, from these experiments, that light from 
a bright cloud, if allowed to act on the eye repeatedly dunng 
from ;}5 to 74; of a second, developes subjective colors; ta 
however, the development of the subjective tint is dependent. 
not so much on the length of time which the eye is exposed, 8s 
upon the interval of rest or shade which follows each exposul® 
may be shown in the following manner: In the experimen? 
where with 114 revolutions a reddish purple was produced, the 
exposure lasted 51, of a second; the interval of rest oF shade. 
was ;'; of a second; now a disc was cut similar to fig. }; 
having eight slits, each 7° 12’ in width, when it:was found that 
5°d instead of 11:5 revolutions per second produced the purplish: 
red tint; here the exposure was twice as long, but the interv! 
of rest or shade nearly the same. With sixteen slits, 23's revolt: 
tions produced the same tint, the exposure being of course fout 
mes as long, but the interval of rest nearly the same. Deter 
minations of the length of this interval are given below:— 
Length of the intervals of shade required for the production of — a, 
rs Biue,. ry ye eee eee eee ht ee bre beccstoerte te sec. ~ : 
Ns Purplish-red, . eae ee ee ee ee ee ae ee ee sy e : 
To ascertain exactly what portions of these intervals elapse 
4 
