308 Intelligence and Miscellaneous Articles. 



when becoming a trifle loose. The brightest musses seem to be 

 higher and therefore thicker than the others ; the brightness of the 

 lower and thinner parts being modified by the decidedly inferior 

 luminosity of the second or penumbral stratum, which is, as it were, 

 partially seen through it. This idea would seem to be greatly 

 strengthened by the fact that the remarkably bright streaks called 

 faculcB are undoubtedly ridges, being elevated to a considerable 

 extent above the general surface, — of which I have had ocular de- 

 monstration on more than one occasion by their actual projection at 

 the limb of the sun, like an irregular range of hills at the edge of the 

 moon, as well as by their frequently, either partially or entirely, 

 concealing openings which have soon been brought into view by the 

 sun's rotation. 



However plausible this conclusion may appear, there are two facts 

 which strongly militate against it. One is, that the less luminous 

 masses are seen to the very edge of the sun, both near the equator and 

 at the poles, except when, near the equatorial edge, they are concealed 

 by obvious faculse. This seems to be quite inconsistent with their 

 being to any considerable extent depressed below the brighter masses, 

 sufficiently so at least to produce so great a difference in their bright- 

 ness. The second fact is, that the boundaries between the two kinds 

 of masses referred to are too abrupt, and the change of brightness 

 too sudden, to allow of anything like gentle undulations. The sides 

 of the brighter portions must be almost precipitous to produce the 

 views we obtain of them under the finest circumstances. 



From these facts I have been led to the conclusion that the masses 

 of inferior brightness, though self-luminous like the brighter, are so 

 far different in their nature that the two do not readily mingle together, 

 and that it is only at their confines that they do so at all ; and also 

 that their surfaces are on the whole at the same level — the principal 

 exceptions being found in the faculce, which are formed entirely of 

 the brighter portions. Those which are less luminous may on that 

 account be more transparent, and perhaps also less dense, and there- 

 fore more readily permitting the escape of some non-inflammable gas 

 producing the pores or fissures occasionally found in them. 



The apparent mottling on the sun's surface is obviously produced 

 by the juxtaposition of the more and less luminous masses or clouds ; 

 and I must confess myself quite unable to perceive how such a con- 

 dition can be compatible with a pretty uniform distribution of lumi- 

 nous masses of any one shape or degree of brightness. The fine 

 mottling is a certain fact, easily verified with a very moderate 

 amount of instrumental aid, and subject to no suspicion of being an 

 optical deception. It certainly seems to me, therefore, that a proper 

 degree of caution may well make us hesitate to admit as a fact any 

 appearance obviously incompatible with it, only rarely seen by very 

 few, and never once perceived by others during years of the most 

 careful scrutiny under the most favourable circumstances and with 

 optical means perfectly adapted to the purpose. 



We may now proceed to consider the cause and mode of formation 

 of the different kinds of solar spots. Any one accustomed to observe 



