282 Proceedings of Metropolitan Societies. | April, 
either rapidly enlarging or closing. Jt is under these circumstances 
especially that the luminous masses are found to become more elongated. 
This is also more remarkably the case when they are preparing for a 
rush across a chasm, and thus forming those luminous bridges which 
so often intersect considerable spots.” 
After detailing some more facts connected with the formation of 
these luminous bridges, the author draws attention to the distinction 
between the true or blacker nucleus, and the wmbra. In almost all 
large spots the former is found to occupy some portion of the latter ; 
and the author thinks that the establishment of the fact of the exist- 
ence or absence of such black nucleus is “ sufficient to determine, or 
at least to throw much light upon the origin of the spot; and that 
the origin of those in which the nucleus exists is widely different from 
the origin of those from which it is absent.” 
The author’s second paper on the same subject, delivered in January, 
was to some extent a recapitulation of the first, after which he proceeded 
to communicate further details concerning the solar spots. 
These he divides into two classes, which he names the profouneé and 
the superficial ; and thus describes the characteristics of each. 
“The profound.—In this class I should include those which give 
evidence of involving all the visible envelopes, the disturbance being 
observable through them all, and down to what appears to be the body 
of the sun itself.” 
“The superficial spots—These appear, from the general tenour of 
my observations, to be almost always produced by convulsions of some 
kind in the photosphere itself, or at a small depth below it. But, 
from the extraordinary variety of the effects, I confess that I am not 
prepared to add anything to the suggestions already advanced as to the 
character of those convulsions, or the means by which they may be 
produced.” 
With regard to the probable formation of the profound spots, Mr. 
Dawes arrives at the following conclusions :— 
“An immense volume of some non-inflammable gas, discharged 
with prodigious force from the body of the sun by volcanic or some 
similar agency, bursts through the cloudy stratum, rolling back on all 
sides the displaced portion of that stratum, and producing that heaped-up 
appearance at its inner and lighter edge. The black hole produced 
in the stratum by this volcanic eruption forms the nucleus of the spot.” 
** Having passed through the cloudy stratum, the evolved gas comes 
within the influence of the heating power of the self-luminous penum- 
bral stratum ; and being greatly expanded thereby, its increased volume 
removes a far larger area of this second stratum than of the first ; thus 
laying bare a considerable portion of the upper surface of the cloudy 
stratum, and producing the wmbra of the spot. Here, too, the rolling 
back of the removed portion causes a heaped-up and brighter appear- 
ance at the inner edge of the penumbra. Being still further heated, and 
expanded by approaching the photosphere, a similar effect is produced 
upon this upper stratum, but to a far greater extent; and a much 
larger portion of the photosphere is thrown off on all sides, which 
being, as before, rolled back upon the rest, gives the appearance of a 
