1864. | Henscunn on the Solar Spots. 223 
or furrowed appearance in the penumbre, directed always radially to or 
from the centre of the umbra, as if rifted, and allowing the black ground 
on which they are seen projected to appear through the chinks (see 
Fig. 3): an appearance likened in certain cases by Mr. Dawes to “ bits 
of straw,” and by Mr. Nasmyth asserted to be distinctly referable to 
certain fusiform, lanceolate, or “‘ willow-leafed” objects of definite size 
and shape, superposed in general like scales, covering one another par- 
tially (see Fig. 5), but in the penumbra, radially arranged, of which he 
conceives the whole luminous surface of the sun to consist.* It is not 
meant to assert that either the penumbre or umbrz are devoid of all 
gradation of light. Both have darker and lighter shades, but 
(especially as regards the umbrze) within far narrower limits of varia- 
tion. Within the latter, indeed, which, up to a recent period, most ob- 
servers, after Sir William Herschel, lad agreed to regard as openings 
through which the dark body of the solar globe could be seen, Mr. 
Dawes, by the application of his diaphragm eye-piece already mentioned, 
has disclosed the existence of a third, and still deeper definite shade of 
darkness, constituting, as it were, a nucleus, or umbra of the second 
order (see Fig. 3), to which we propose henceforward to restrict the name 
of “nucleus.” Between the penumbra, too, and the general brightness 
of the photosphere, a suddenness of transition exists, less marked, in- 
deed, than that between it and the nucleus, and less rigidly preserved, 
but yet on the whole exceedingly striking. And the whole series of 
phenomena strongly suggests the notion of three envelopes or veils 
between the exterior transparent atmosphere and the sun itself, the 
two outer being luminous, the inner probably only seen by reflected 
light ;—each capable of being partially removed, either by some emana- 
tion or upsurging movement from below, or denudation from above, 
leaving a central opening, over which, when the denuding cause has 
ceased its action, the luminous strata tend to return, and spread them- 
selves equally. Even in such central opening, however, the darkness 
is probably only relative, and, could the surrounding glare be com- 
pletely extinguished, the light of the central space would probably 
equal or exceed that of the brighter incandescence of our furnaces. It 
is inconceivable indeed, that the actual surface of the solar globe (if 
there be any such definite surface), surrounded as it is by an enceinte of 
such a temperature as that of the photosphere, should be otherwise 
than in a state of the most vivid incandescence: and that it should 
appear no brighter than it does is not the least inexplicable feature of 
solar physics. Can it be that the interposition of mixed metallic 
vapours, each specifically opaque to definite rays of the spectrum be- 
tween the body and the penumbral envelope may by their joint absorp- 
tion, cut off nearly the whole of the light of the former? Ignited, 
transparent, and colourless liquids or gases, it should be observed, 
give off no light from their interior. 
The forms of the spots are extremely irregular; of the penumbra 
* Other observers, as I have recently been informed, consider Mr. Nasmyth’s 
“‘ willow-leaf” figures as too slender and pointed, and liken the forms rather to 
that of rice-grains. 
