. 
C. S. Hastings— Constitution of the Sun. 37 
There is, however, a fatal objection to the explanation as 
given by this theory. If the luminous particles are precipitated 
from the vapors of the photosphere, they cannot be at a higher 
temperature than the cireumambient gases; on the contrary, 
on account of their greater radiating power they must be 
slightly cooler. But the fundamental theory of absorption 
demands a lower temperature for the vapor producing dar 
lines than that of the principal source of light behind it; con- 
sequently this view of Faye cannot be accepted without great 
modifications. 
Before advancing any theory of my own, it may be well to 
» emphasize two principles taught by the theory of absorption, 
to which all hypotheses must be conformable. That Faye’s 
fails in this is sufficient cause for its rejection. 
1st. To produce dark lines in a spectrum by absorption, the 
source of absorbed light must be at a higher temperature than 
that of the absorbing medium. 
. There is an inferior limit of brightness below which the 
course of absorbed light cannot go without the spectral lines 
becoming bright. 
Of these, the first is familiar and requires here neither proof 
nor comment; the second, though not less evident, is less 
familiar because less important. As we shall make use of it, 
however, it may be well to enforce it by reference to common 
experience. Were it not true it would be impossible to see 
bright lines in the spectrum of any flame to which daylight 
had access, for in this case the conditions demanded by the 
first principle are fully met, the sun being the origin of the 
daylight. That we do not see absorption lines is due then 
alone to the lack of necessary brilliancy in the daylight. _ 
‘hus much premised we can frame a theory which explains 
all the observed phenomena exhibited by the spectroscope, and 
1s also rendered highly probable by the revelations of the 
telesco 
As is well known, the solar surface when examined with a 
powerful telescope of large aperture presents a granulated ap- 
pearance, the granules in general subtending an angle of a frac- 
tion of a second only. Probably this appearance is better known 
to the majority of astromoners by means of Professor Langley’s 
admirable drawings* rather than by personal observation. These 
granules I regard as marking the locus of currents directed 
generally from the center of the sun. About these currents 
are necessarily currents in an opposite direction which serve to 
maintain a general equilibrium in the distribution of mass. 
Let us consider the action of such an ascending current. Start- 
ing from a low level at a temperature which we may regard as 
* This Jour., vol. vii, 1874, and vol. ix, 1875. Plates. 
