ME. J. N. LOCKYEE ON SPECTEOSCOPIC OBSEEYATIONS OE THE SUN. 437 
remarking here that there is nothing said about the “ clouds ” forming a continuous 
envelope round the sun. 
Professor Grant*, who went over the same ground as Arago, and had Arago’s results 
before him, was led to consider before the eclipse of 1851 that “The observations of 
solar eclipses would seem to indicate that above the luminiferous envelope there exists 
a stratum of nebulous matter which is visible only by means of reflected light. Various 
interesting questions present themselves for solution in connexion with the admitted 
existence of such a stratum. In the first place, does this third envelope exercise an 
influence in the production of any of the other phenomena which have been disclosed 
by observations on the physical constitution of the sunl” 
Then, referring to Sir J. Herschel’s hypothesis of convection currents throwing up 
the then imagined non-luminous envelope below the photosphere, through the photo- 
sphere, he adds : — 
“ This view of the subject, while it carries with it considerable probability, obviates 
the necessity of introducing into the theory of the physical constitution of the sun the 
idea of a third envelope independent of the two others.” 
We next come to the eclipse of 1851, which was observed by Professor Swan, among 
others, who contributed to the Eoyal Society of Edinburgh three valuable memoirs on 
the eclipse with special reference to the red prominences. Assuming that they existed 
in the solar atmosphere, and agreeing with the prescient remarks of Sir J. Herschel, 
that they must be “cloudy masses of the most excessive tenuity,” he remarksf : — 
“ Obviously the simplest view that can be taken of this phenomenon, is to regard the 
red fringe and the red prominences as of the same nature ; and all the observations will 
then confirm the idea that the matter composing those objects is distributed all round 
the sun. It therefore seems probable that when we are furnished with observations of 
a tangential phase of the eclipse from stations on the north side of the moon’s shadow, 
it will be found that a sierra appeared towards the sun’s north point, of which the detached 
prominences seen in that region, by observers situated near the middle of the moon’s 
shadow, were only the highest peaks Since, then, it has been 
shown to be highly probable that the matter composing the red prominences is distributed 
with little interruption all round the sun, we may conceive the luminous strata of the 
solar atmosphere to be surmounted by an envelope of clouds of which the higher 
portions are visible beyond the moon’s limb, at the central phase of a total eclipse, and 
which then constitute the red prominences. If [he continues, throwing out the sug- 
gestion previously made by Grant] it be thought that the hypothesis of two envelopes of 
cloud, one above and another below the luminous strata of the sun’s atmosphere, intro- 
duces too great complication, we may avoid the objection by supposing that the envelope 
which occasions the penumbras around the spots penetrates the luminous stratum, and 
exists, although in greatly different degrees of density, both above and below it. 
* History of Physical Astronomy, p. 400. 
f Transactions of the Eoyal Society of Edinburgh, vol. xx. part iii. pp. 462, 463, 464. 
