472 MR WILLIAM SWAN ON THE 
occuperaient les nuages de la troisicme enveloppe? Peut-ctre ces nuages produi- 
sent-ils les pénombres isolées, les pénombres sans noyau. Les taches de ce genre 
ne sont pas trés-communes; jamais leur étendue totale n’est un partie aliquote 
considerable de la surface solaire.”* 
From these passages, it appears that in M. AraGo’s opinion, the sun, besides 
being surrounded by a stratum of dark clouds, and a photosphere, has, beyond 
them, and enveloping them, a third atmosphere, in which are floating clouds, 
which, when seen during a total eclipse, form the red prominences. 
This is the same view as that stated at the beginning of my paper, on the autho- 
rity of Sir Joun Herscuet, and to which I have ventured to add the hypothesis 
that the clouds causing the prominences form of themselves a nearly continuous 
envelope, floating in the third atmosphere, and above the photosphere. If, then, a. 
formal enumeration of the sun’s envelopes were made, according to my view there 
would be four. Ist, The dark clouds below the photosphere. 2d, The photosphere 
itself. 3d, The envelope of cloud so often referred to; and, 4¢h, The sun’s atmo- 
sphere surrounding all, and in which the other three solar envelopes may be sup- 
posed to float. 
That M. Araco does not regard the clouds which occasion the red prominen- 
ces as forming a continuous envelope, appears evident from several considerations. 
In enumerating the envelopes surrounding the sun, he never mentions more 
than three,—viz., the cloudy envelope below the phcetosphere, the photosphere 
itself, and a third atmosphere surrounding it. This third atmosphere is also 
spoken of as a third envelope, and as an exterior envelope; but these different 
expressions are evidently employed to denote, as one envelope, the sun’s exterior 
atmosphere, along with the clouds floating im it; for if the atmosphere and the 
clouds were reckoned separately, there would be jour envelopes and not three. 
The passage where the third envelope is said to be formed of clouds (formée de 
nuages) would, indeed, if read by itself, seem to convey the idea of an envelope, 
composed of clouds exclusively ; but other passages sufficiently prove that this is 
not M. Araao’s view. Thus the expression, “ the clouds of the third’ envelope” 
indicates the idea that those clouds are not themselves the envelope, but detached 
masses floating init. Moreover, since the terms, third envelope, third atmosphere, 
and exterior envelope, are obviously all used in the same sense,—the exterior 
envelope or third envelope cannot consist alone of a continuous stratum of clouds 
forming the red prominences; for it is elsewhere described as causing the white 
corona (cowronne blanchdtre), which, in the case supposed, would be red, and not 
white. 
It seems also highly probable, that if M. AraGo had supposed that the clouds 
forming the red prominences also constitute a continuous stratum surrounding 
the sun, the phenomenon of a band of red light seen at the end of the total phase 
of solar eclipses,—which he believes} is caused by the presence of red promi- 
* Annuaire for 1846, p. 465. + Ibid. for 1842, p. 440, et seq. 

