S. P. Langley—The Solar Atmosphere. 493 
from near the edge is juxtaposed with that from the center, the 
shadow illuminated by the former is chocolate-red,* while that 
from the latter is a peculiar bluish tint, nearly like that given 
by the shade-glass called by English opticians ‘London 
Smoke.” (I use these comparisons not being able readily to as- 
similate these colorsto any of the pure spectrum.) It is worth 
while to remark that this observation confirms others obtained 
changes in apparent magnitude, would lead us away from the 
present subject. 
_ So clear an exhibition of color in the actual comparison is a 
sign of the delicacy of the Rumford method, but it introduces a 
disturbance in our estimation of the intensities of colored 
strument ; and in practice corrections for every form of instru- 
mental error are applied which are not here mentioned. 
The methods above indicated are, with some slight modifi- 
cations, evidently adapted to the comparison of the hght of the 
Sun-spots, and the light adjacent to the limb, with that of the 
center; to studying the rate of diminution of light without the 
dise, and to like investigations ; and they are now being so used. 
* This color appears to have passed unnoticed by all observers but Secchi, who 
Temarks that the edge of the disc is smoky-red. 
