370 CS. Hastings—Spectra of the Limb and Center of the Sun. 
figure, in which ss’ is the slit, LL/ the diameter of the sun’s 
image, and P the prism, shews that 
no light from the covered part of 
the slit will reach the collimating 
lens except that which has been 
reflected from the two sides of the 
prism. The relation of the acute 
angle (v) and the distance between 
the reflecting sides (?) to the focal 
length of the great telescope (/’) and the width of the spectrum 
(a) is given by the formula, 
2¢ sin v = F tan 16’—a. 
the center of the sun’s disk, but disappears entirely, to MY 
ower at least, within 16” to 20” from the limb. , 
nes below F, at 1828-6 and 1830-9 of the same scale, exhibit 
i t 
marked near the edge, but much fainter at the center. These 
latter lines also become greatly strengthened over the penum- 
b affected. These are 
ae ree of spots. The line 768°1 is not thus affected 
yo 
