NATURAL PHILOSOPHY. 173 



t 



throughout the whole mass; and if the atmosphere ever had been 

 cold, it is clear that in the course of ages it must have become in- 

 tensely heated. This atmosphere must act on the nucleus in the same 

 way as the photosphere acts upon it ; the nucleus must likewise be- 

 come heated to the point of incandescence. It must therefore give 

 off light and heat ; for all bodies begin to glow at the same tempera- 

 ture." Kirchhojf; Researches, etc., pp. 25, 26. 



Our author then proceeds to account for the phenomena of the 

 solar spots by the supposition of two superimposed layers of clouds 

 being formed in the solar atmosphere. One of these, being dense 

 and near the sun's surface, does not allow the light of the underlying 

 portion of the sun to pass, and forms the nucleus of the spot ; whilst 

 the other, being produced at a higher elevation, is less dense, and 

 forms what we term the penumbra. 



It is unfortunate for Kirchhoff's theory that the unanimous verdict 

 of all who have examined these singular phenomena is in favor of 

 their being funnel-shaped depressions. Preconceived notions have, 

 however, so powerful an influence over the mind, and it is so difficult 

 to obtain a truthful estimate of relative depression and elevation 

 at such distances, that we are willing to believe that astronomers 

 may possibly be mistaken in their views on this subject. There is, 

 however, one method of observation which would seem qualified to 

 settle the disputed question. If the astronomers' view of the con- 

 struction of the spots is correct, the dark nucleus never can be seen 

 beyond the penumbra, when the spot moves round towards the sun's 

 limb. On Kirchhoff's view such a separation of the two clouds form- 

 ing nucleus and penumbra is perfectly possible, and when they have 

 nearly reached the edge of the sun's disc, we ought to see the dark 

 cloud below, and separate from the upper one. Such a separation, 

 however, has not been noticed ; and, on the other hand, we may ad- 

 duce the following observation of Sir William Herschc-1, as leading 

 to a directly opposite conclusion : 



"Oct. 13, 1794. The spot in the sun I observed yesterday is 

 drawn so near the margin that the elevated side of the following 

 part of it hides all the black ground, and still leaves the cavity visi- 

 ble, so that the depression of the black spots and the elevation of 

 the facula? are equally evident." 



The more the question of the physical constitution of the sun is 

 considered, the more does it appear that we have no right to make 

 up our minds concerning it, either in one way or the other. Seeing 

 how Jjttle is really known about the matter, with the true spirit of 

 scientific inquirers, we hold ourselves open to conviction as soon as 

 satisfactory evidence shall be brought forward. The singular obser- 

 vations first made by Mr. James Nasmyth, a few months ago, con- 

 cerning the physical condition of the sun's surface, observations so 

 novel ^that astronomers were loth to receive them as facts until they 

 were confirmed by other observers, need only to be mentioned in 

 order to show that we are not in a position to uphold any theory 

 whatever of the physical constitution of our great luminary. Mr. 

 Nasmyth asserts, and his assertion has been confirmed by the sub- 

 sequent observations of more than one competent observer, that the 

 15* 



