Intelligence and Miscellaneous Articles, 309 



them, even in the most cursory way, must have been struck, not 

 only with the endless variety of their forms, but also with an essen- 

 tial difference in their character. For our present purpose they 

 may perhaps be most suitably divided into two classes, the profound 

 and the superficial. 



1. The prof 'ound. — 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. Among the envelopes I do not include any 

 exterior to the photosphere, but restrict the term to the three which 

 I have already referred to, but will here more particularly specify. 



The first in order from the body of the sun outwards is what, in 

 my e Description of a new Solar Eyepiece,' I pointed out as being 

 really an envelope, and not the body of the sun, as it had been pre- 

 viously accounted and as such had been generally called the nucleus 

 when it occupied the middle of a spot. By using a field of view 

 sufficiently small to exclude even the penumbra of pretty large spots, 

 and using as light a glass as the eye can comfortably bear, a mottled 

 appearance is perceived in this stratum, the degree of darkness being 

 by no means uniform, and suggesting the idea that the surface we 

 see is far from level — the lighter parts being probably the most ele- 

 vated, and feebly reflecting the light received from the self-luminous 

 strata above it. To this lowest envelope I applied the term cloudy 

 stratum, forming the umbra of a spot. In all spots which are tole- 

 rably symmetrical, and large enough to admit of accurate scrutiny, 

 the umbra will be found to be perforated near its centre by a perfectly 

 black hole which I regard as the true nucleus. The form of the 

 umbra usually approximates to that of the nucleus, being nearly 

 round when the nucleus is so ; and when the nucleus is much elon- 

 gated, or when some part of it greatly varies in shape from the rest, 

 the general form of the umbra is almost constantly found to partake 

 of a similar irregularity. A very remarkable feature of this cloudy 

 umbra is, that at the edge next to the nucleus it is usually decidedly 

 less dark thata. elsewhere, giving the impression of being there more 

 elevated or heaped up. This is especially the case with spots which 

 have only recently broken out, or are in the process of enlargement. 

 On the contrary, when a spot is closing up, this feature disappears. 

 Occasionally some very small bright specks are visible on this stra- 

 trum ; but I believe they do not belong to it at all, but are minute 

 portions of one of the self-luminous strata above it. 



The second or middle envelope constitutes the penumbra which 

 usually attends all spots of considerable size and symmetrical forms. 

 It possesses, I think, all the characters of self-luminosity, though its 

 brightness is far inferior to that of the outer envelope. In most cases 

 lines of much greater brightness are projected upon it, which obvi- 

 ously belong to the outer one, or photosphere. But occasionally 

 some parts of the penumbra, especially where it is very broad, are 

 decidedly brighter than the rest, and these are rarely, if ever, over- 

 laid with the bright lines from the photosphere. They give me the 

 impression of belonging, not to the penumbral stratum at all, but to 



