494 S. P,. Langley—The Solar Atmosphere. 
there is within the umbra a sensibly black “ neucleus,” and 
from the assumed blackness of this “ neucleus,” several astron- 
omers have been led to suppose that the “neuclei” are not 
openings into a dark gaseous interior. 
The measurement of umbre, and of so-called “ neuclei” here 
shows not only that neither are absolutely dark, but that the ab- 
solute light of either is enormous, that of the average “ neucleus,” 
so-called, being, as I find, at least jive thousand times that of the 
n. 
La Place, in assuming that the radiation in any direction is 
constant, and is proportional to the radiating area (or that the 
radiation is infinite at the edge of the disc), concludes that the 
total absorption is represented by the integra 
1 a 
anf. @ 0088 sindd 6 
o 
where @ is the heliocentric angle between the earth and the 
point of the solar surface under examination; and this assump- 
tion has been adopted by Father Secchi, who, in his latest 
edition of Le Soleil, gives results derived from the use of this 
integral. I shall, however, assume, in accordance with what 
seem to be the teachings of modern physics, that a globe as 
large as the sun whose photosphere, though composed perba 
of very light vaporous material, is yet opake at a limited depth, 
(as observations on superposition of cloud-strata have shown) 
that in such a globe radiation would be proportional to the co- 
These expressions, if La Place’s assumptions are otherwise 
correct, should give, for any comparison of the heat at a given 
point of the dise to that of the center, a certain value of the 
absorption which should be constant for any value of 4 In 
The discre| 
fact I find, however, that this is not the case. 
