
RED PROMINENCES SEEN DURING TOTAL ECLIPSES OF THE SUN. 463 
through apertures, such as 7 / fig. 10, in a luminous envelope, @ 6, which surrounds 
him; and Sir Witu1am Herscuet,* to explain the penumbra which generally en- 
circles a solar spot, considers the luminous strata to be sustained far above the 
level of the sun’s solid body, by a transparent elastic medium, carrying on its 
upper surface (or rather at some considerably lower level within its depth) a cloudy 
stratum c d, which being strongly illuminated from above, reflects a considerable 
portion of light to our eyes, and forms the penumbra, while the solid body shaded by 
the clouds reflects none. The temporary removal of both strata, but more of the 
upper than the lower, as represented in the figure, he supposes effected by power- 
ful upward currents of the atmosphere, arising, perhaps, from spiracles in the 
body, or from local agitations.} 
Since, then, it has been shewn to be highly probable that the matter, compos- 
ing 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 (e7,) of clouds, of which only the higher portions are visible beyond 
the moon’s limb, at the central phase of a total eclipse; and which then consti- 
tute the red prominences. If it be thought that the hypothesis of two envelopes 
of cloud, one above and another below the luminous strata of the sun’s atmo- 
sphere, introduces too great complication, we may avoid the objection, by sup- 
posing that the envelope which occasions the penumbree around the spots pene- 
trates the luminous stratum, and exists, although in greatly different degrees of 
density, both above and below it. 
If, then, we conceive that a stratum of cloudy matter surrounds the sun, of 
which the red prominences are the higher portions, the serrated appearance of 
the long range of prominences, seen by Mr Dawes and Mr Hin), sufficiently indi- 
cates that its general surface is exceedingly uneven, presenting the appearance of 
being covered with numerous eminences or ridges. But these irregularities are 
small when compared with the large hook-shaped prominence, and its companion 
the detached cloud, which were seen by most of the observers of the eclipse. The 
altitude of the hook-shaped prominence has been variously estimated at from 15 
to 3’; and, by actual micrometrical measurement, it was found to be 1’ 41""5 just 
before the sun reappeared.} Adopting this measurement, its actual height must 
have exceeded 47,000 miles, or about six times the diameter of the earth. The 
existence of bodies of such magnitude indicates some immense local disturbance in 
the sun’s atmosphere, but not greater than that indicated by the solar spots, some 
of which Sir Joun Herscuet states to have been observed, “ whose linear dia- 
meter has been upwards of 45,000 miles, and even, if some records are to be 
* Philosophical Transactions, 1801. + Herscuex’s Outlines of Astronomy, par. 389. 
t This is the mean of observations by Mr Wriiurams and Mr Srannistrezt. Notice of R. Ast. 
Soc, for January 1852, pp. 54, 55. 
