36 C. S. Hastings— Constitution of the Sun. 
This evident consequence, pointe out e first plac 
is but one way of maintaining the theory and escaping Forbes’s 
conclusion already’ quoted, and that the course pursued by 
Kirchhoff in the original statement of his theory of the solar 
constitution,* namely, by assuming that the depth of tne re- 
versing atmosphere is not small compared to the radius of the 
sun. But innumerable observations during the score of years 
which have lapsed since that time prove that such a reversing 
atmosphere must be very thin. The famous observation of 
hoff’s views as to the locus of the origin of the dark lines. 
But this very a restricts the effective atmosphere 
(save for hydrogen and one or two other substances) to a depth 
not more than 2”. hus, singularly enough, the very 
observation, which led to the firmest beliéf among spectroscop- 
ists in the correctness of Kirchhoff’s view, exposed at the same 
time its most vulnerable point. 
nother theory of the solar constitution, that of Faye, 
assigns a different seat to the stratum producing the Fraunho- 
fer lines, namely, the photosphere itself. Regarding the prin- 
cipal radiation of the sun as com ming from solid or liquid 
particles floating in a gaseous medium, the cloud-like stratum 
thus formed is necessarily somewhat transparent. According 
to his views, these particles are the sources of the continuous 
spectrum, and the medium in which they float is the locus of 
the selective absorption.t Thus he attempts to reconcile the 
 ialagy theory of Kirchhoff with the annette and deduc- 
tio Forbes, which, as we have were a constant 
prembling block in the way of arent Kirchhoff” s explana- 
tion. 
ockyer seems to have accepted this theory, and to have 
defended it in the earlier portion of his work ;{ but in _ 
after Young’s important observation of 1870 and its confirm 
tion in 1871, he changed his views and regarded the layer just 
outside the photosphere as the true seat of the selective absorp- 
tion producing the Fraunhofer lines.§ I supposed in 1873 that 
my observations then published could be explained on Faye’s 
hy pothesis. 
* Untersuchungen vee das bot ong magica Berlin, 1862, pp. 14-15. 
+ Comptes Rendus, vol. 
See “ A lecture dauwnres the Royal Institution,” May 28th, 1869. Quoted 
in Lockyer’s Solar Physics, pp. 220-221; — ‘The Rede Lecture, ” May 24th, 
1871. Quoted in Solar Physics, pp. 317-3 
§ See revised report of two anne pee at Neweastle-upon-Tyne in 
October, 1879, Solar Physics, p. 4 
