SCENES ON THE PLANETS. 341 



western edge of the disk, gradually losing their distinctness and 

 altering their appearance, while from the region of indistinct defi- 

 nition near the eastern edge other markings slowly emerge and 

 advance toward the center, becoming sharper in outline and more 

 clearly defined in color as they swing into view. 



Watching these changes, the observer is carried away by the 

 reflection that he actually sees the turning of another distant world 

 upon its axis of rotation, just as he might view the revolving earth 

 from a standpoint on the moon. Belts of reddish clouds, many 

 thousands of miles across, are stretched along on each side of the 

 equator of the great planet he is watching; the equatorial belt 

 itself, brilliantly lemon-hued, or sometimes ruddy, is diversified 

 with white globular and balloon-shaped masses, which almost re- 

 call the appearance of summer cloud domes hanging over a terres- 

 trial landscape, while toward the poles shadowy expanses of grad- 

 ually deepening blue or blue-gray suggest the comparative cool- 

 ness of those regions which lie always under a low sun. 



After a few nights' observation even the veriest amateur finds 

 himself recognizing certain shapes or appearances — a narrow dark 

 belt running slopingly across the equator from one of the main 

 cloud zones to the other, or a rift in one of the colored bands, or 

 a rotund white mass apparently floating above the equator, or a 

 broad scallop in the edge of a belt like that near the site of the 

 celebrated " red spot," whose changes of color and aspect since its 

 first appearance in 1878, together with the light it has thrown on 

 the constitution of Jupiter's disk, have all but created a new Jovian 

 literature, so thoroughly and so frequently have they been dis- 

 cussed. 



And, having noticed these recurring features, the observer will 

 begin to note their relations to one another, and will thus be led 

 to observe that some of them gradually drift apart, while others 

 drift nearer; and after a time, without any aid from books or 

 hints from observatories, he will discover for himself that there is a 

 law governing the movements on Jupiter's disk. Upon the whole 

 he will find that the swiftest motions are near the equator, and 

 the slowest near the poles, although, if he is persistent and has a 

 good eye and a good instrument, he will note exceptions to this 

 rule, probably arising, as Professor Hough suggests, from differ- 

 ences of altitude in Jupiter's atmosphere. Finally, he will conclude 

 that the colossal globe before him is, exteriorly at least, a vast 

 ball of clouds and vapors, subject to tremendous vicissitudes, pos- 

 sibly intensely heated, and altogether different in its physical con- 

 stitution, although made up of similar elements, from the earth. 

 Then, if he chooses, he can sail off into the delightful cloud-land of 



