Physics. — “On the Effective Temperature of the Sun’. Some 
remarks in connection with an article by Derant: “ Dijf uston 
und Absorption in der Sonnenatmosphdre.” By H. Groot. 
(Communicated by Prof. W. H. Jurius). 
(Communicated in the meeting of March 29, 1919). 
In a paper ‘Ueber Diffusion und Absorption in der Sonnenatmos- 
phare”’ (Sitz. Ber. d. Berl. Akad. 1914) ScuwarzscuiLp treated the 
problem of the radiation: of a plain layer, which must be imagined 
as an absolutely black body, and above which there is an absorbing 
and dispersive atmosphere. When on a layer (see figure 1) bounded 
by the planes =O and «= H radiation of intensity S, starting 
from the black body ZZ’ falls from all directions, ScHwaARZsCHILD 
denotes by b(z,t) the radiation which passes through the plane z 
in the same sense as the radiation S, and at an angle 7 with the 
normal to the boundary layers, and then tries to find a formula 
for 6(0,2). 
Fig. J. 
Black body. 
Accordingly 6(0,2) is the total intensity of light that passes out at 
an angle 7 at the boundary of the atmosphere, and is built up of 
direct light and light that is dispersed once, twice ete. 
SCHWARZSCHILD succeeds in solving this problem for two special 
cases, and finds: 
a. Limiting case of exclusive absorption (6 = 0): 
b cost 
HO =a + — 
(1—e—*H sec t) mt VOID 7 (1) 
