NEWS FROM JUPITER. 441 



It may be asked whether I regard the ruddy glow of Jupiter's equa- 

 torial zone, during the period of disturbance lately passed through, as 

 due to the inherent light of glowing matter underneath his deep and 

 cloud-laden atmosphere. This appears to me on the whole the most 

 probable hypothesis, though it is by no means certain that the ruddy 

 color may not be due to the actual constitution of the planet's vapor- 

 ous atmosphere. In either case, be it noted, we should perceive in 

 this ruddy light the inherent lustre of Jupiter's glowing mass, only in 

 one case we assume that that lustre is itself ruddy, in the other we 

 suppose that light, originally white, shines through ruddy vapor- 

 masses. It is to be remembered, however, that, whichever view we 

 adopt, we must assume that a considerable portion of the light re- 

 ceived, even from these portions of the planet's disk, must have been 

 reflected sunlight. In fact, from what we know about the actual 

 quantity of light received from Jupiter, we may be quite certain that 

 no very large portion of that light is inherent. Jupiter shines about 

 as brightly as if he were a giant cumulus-cloud, and therefore almost 

 as white as driven snow. Thus he sends us much more light than a 

 globe of equal size of sandstone, or granite, or any known kind of 

 earth. We get from him about three times as much light as a globe 

 like our moon in substance, but as large as Jupiter, and placed where 

 Jupiter is, would reflect toward the earth ; but not quite so much as 

 we should receive from a globe of pure snow of the same size and 

 similarly placed. It is only because large parts of the surface of 

 Jupiter are manifestly not white, that we seem compelled to assume 

 that some portion of his light is inherent. But the theory that Jupiter 

 is intensely hot by no means requires, as some mistakenly imagine, 

 that he should give out a large proportion of light. His real solid 

 or liquid globe (if he have any) might, for instance, be at a white 

 heat, and yet so completely cloud-enwrapped that none of its light 

 could reach us. Or, again, his real surface might be like red-hot 

 iron, giving out much heat but very little light. 



I shall close the present statement of evidence in favor of what I 

 begin to regard as in effect a demonstrated theory, with the account 

 of certain appearances which have been presented by Jupiter's fourth 

 satellite during recent transits across the face of the planet. The ap- 

 pearances referred to have been observed by several telescopists, but 

 I will select an account given in the monthly notices of the Astro- 

 nomical Society, by Mr. Roberts, F.R. A. S., who observed the planet 

 with a fine telescope by Wray, eight inches in aperture. " On March 

 26, 1873," he says, "I observed Jupiter about 8 p. m., and found the 

 fourth satellite on the disk. I thought at first it must be a shadow ; 

 but, on referring to the Nautical Almanac, found that it was the 

 fourth satellite itself. A friend was observing with me, and we both 

 agreed that it was a very intense black, and also was not quite round. 

 We each made independent drawings, which agreed perfectly, and 

 consider that the observation was a perfectly reliable one. We could 



