Notices respecting New Books. 307 



parallel to the equator, with a calm equatorial zone interposed. It 

 only remains, therefore, to inquire, Whether any such cause of cir- 

 culation can be found in the ceconomy of the sun, so far as we know 

 and can understand it ?" 



In answer to this inquiry he observes, that if any physical differ- 

 ence in the constitution or circumferences of the sun's polar and 

 equatorial regions tends to repress the escape of heat in the one, and 

 to favour it in the other of these regions, the effect will be the same 

 as if those regions were unequally heated from without, and all the 

 phenomena of trade-winds, mutatis mutandis, must arise. That the 

 sun is surrounded by a transparent atmosphere, extending beyond 

 its luminous surface, Sir John holds to be conclusively established 

 by various phenomena, and he instances in particular the striking 

 deficiency of light at the borders of the visible disc, and the extra- 

 ordinary phenomenon of the rose-coloured clouds witnessed during 

 the total eclipse of July 8, 1842, which must have floated in and 

 been sustained by an exterior transparent atmosphere. He also 

 thinks that the distance to which this atmosphere extends beyond 

 the visible disc must be considerable, not merely in absolute measure, 

 but as an aliquot part of the sun's radius. " Now, granting the ex- 

 istence of such an atmosphere, its form in obedience to the laws of 

 equilibrium must be that of an oblate spheroid, the ellipticities of 

 whose strata differ from each other and from that of the nucleus. 

 Consequently, the equatorial portions of this envelope must be of a 

 thickness different from that of the polar, density for density, so that 

 a different obstacle must be thereby opposed to the escape of heat 

 from the equatorial and the polar regions of the sun. The former, 

 therefore, ought, according to this reasoning, to be habitually main- 

 tained at a different temperature from the latter." 



According to this view of the subject, the spots come to be " assi- 

 milated to those regions on the earth's surface in which, for the 

 moment, hurricanes and tornadoes prevail — the upper stratum being 

 temporarily carried downwards, displacing by its impetus the two 

 strata of luminous matter beneath, .... the upper of course to a 

 greater extent than the lower, and thus wholly or partially denuding 

 the opaque surface of the sun below. Such processes cannot be 

 unaccompanied with vorticose motions, which, left to themselves, die 

 away by degrees and dissipate, with this peculiarity, that their lower 

 portions come to rest more speedily than their upper, by reason of 

 the greater resistance below, as well as the remoteness from the point 

 of action, which lies in a higher region, so that their centre (as seen 

 in our water-spouts, which are nothing but small tornadoes) ap- 

 pears to retreat upwards. Now this agrees perfectly with what is 

 observed during the obliteration of the solar spots, which appear as 

 if filled in by the collapse of their sides, the penumbra closing in 

 upon the spot and disappearing after it." — P. 434. 



Some appearances which were frequently noticed in the course of 

 these observations might seem at first sight to militate against this 

 idea. Lines of spots of more or less extent, or connected with pe- 

 numbral trains more or less beset with spots, were frequently noticed 



