J. H. Lane on the Theoretical Temperature of the Sun. 65 
face. The temperature of the radiating surface calculated 
from this datum by the formula of Dulong and Petit, and 
with the co-efficient of radiation found by Prof. W. Hopkins 
for sandstone, the smallest co-efficient he found, is 1550° C. or 
2820° Fah. But then the solar radiation is many thousands 
of times greater than the greatest in Dulong and Petit’s experi- 
ments, so that these calculations of the temperature of the sun’s 
photosphere have little weight notwithstanding the simplicity 
and accuracy with which the formula represents the experiments 
which it was derived. Nothing authorizes us to accept 
the formula as more than an empirical one. It seems desirable 
the hydro-oxygen — and the recorded effects of Parker’s 
ens. am not aware that this method has 
before been resorted to. 
If the angle of aperture at the focus of a burning lens, or 
combination of lenses, be called 2a, the radiation received by a 
at surface at the focus will be sin*a, if a unit be taken 
to represent the radiation the same small flat surface would 
receive a at the sun’s surface. Parker’s lens, with the small 
lens ad at the focus so formed, an angle of aperture of 
about 47°. A small flat surface at its focus would therefore 
receive about one-sixth the radiation that it would just at the 
sun, making no allowance for absorption by the atmospheres of 
Am, Jour. Sc1.—SzconpD Series, Vou. L, No, 148.—Juxy, 1870. 
5 
