for the Advancement of Science. oe 
with a Nicols’s prism. A rad’ glass eve 2 no trace of brushes, A 
brownish yellow glass, which absorbed only small. quantity of “ig, 
rendered the brushes very indistinct. A padi gs enabled the 
tity | of light sheathed. ith the green and blue ia ie the brus 
were*not colored, but Seiphy darker than the rest.of the 2 — 
sull further the office of the different, cofors in producing the 
Which was suddenly turned round fr ota tin 1e to time. through about a 
right angle, the author found that the. tnd yellow did not present the ~ 
heteag trace of brushes. The brushes “began to. be visi D ein the green, 
$ faras the line G; aod 
feeble ‘ incapacity of the greater part of the 
Violet to ote homogeneous light, the brushes, when 
they weré formed : at all, were simply darker than the. rest of the field, 
and as might have been « expe ected did not appear of a different tint. ln 
the blue, where the brushi were most distinct, s appeared to the au- 
thor that they were somewhat'shorter than usua hese observations 
ace count at once for the color’ of. the brushes seen om ordinary daylight. 
Aha h as no brushes are seen with the less refrangible colors, and 
inating, on account of its grealer brightness in the solar spectrum. 
The mixture would give an impure yellow, which is the color observed, 
or the cause may be more deeply seated. If the total illumination per- 
ceived be independent of the brushes, the light withdrawn from the 
brushes must be found at their sides, which would account, independ- 
tint of the side patches. The observations with homogeneous light ac- 
count likewise for a circumstance with which the author has been struck, 
Og a that the brushes were not visible by candle-light, which is ex- 
| plained by the comparative poverty of can ndle-light in the more refran- 
gible r rays. The brushes ought to be rendered visible by absorbing a 
specimen of blue glass which showed them best 
tieribty deep color, gave lates which were decidedly red, and were 
_ only comparatively dark, so that the difference of tint between the 
