86 THE POPULAR SCIENCE MONTHLY. 



its turn bringing on a fresh explosion. Now, a rhythmical succes- 

 sion of explosions from the same deep-rooted region of disturbance 

 would produce at the upper level, where we see the expelled vapor- 

 masses (after condensation), a series of rounded clouds lying side by 

 side. For each cloud-mass after its expulsion from a region of slow, 

 absolute, rotational motion, to a region of swifter motion would lag 

 behind with reference to the direction of rotational motion. The 

 earlier it was formed the farther back it would lie. Thus each new 

 cloud-mass would lie somewhat in advance of the one expelled next 

 before it ; and if the explosions occurred regularly, and with a suffi- 

 cient interval between each and the next to allow each expelled 

 cloud-mass to lag by its own full length before the next one appeared, 

 there would be seen precisely such a series of egg-shaped clouds, set 

 side by side, as every careful obseiwer of Jupiter with high tele- 

 scopic powers has from time to time perceived.' 



That these egg-shaped clouds are really egg-shaped not merely 

 oval in the sense in which a flat, elliptic surface is oval is suggested 

 at once by their aspect. But it is more distinctly indicated when de- 

 tails are examined. It appears to me that considerable interest at- 

 taches to some observations which were made by Mr. Brett in April, 

 1874, upon some of the rounded spots then visible upon the planet's 

 equatorial zone. It will not be thought that I am disposed, as a rule, 

 to place too much reliance upon the observations and theories of Mr. 

 Brett, seeing that on more than one occasion I have had to call atten- 

 tion to errors into which, in my judgment, he has fallen. For in- 

 stance, I certainly do not think he has ever seen the solar coi'ona when 

 the sun was not eclipsed, though I have no doubt he saw what he de- 

 scribed, which he supposed to be the corona, but which was in reality 

 not the corona. Nor, again, do I accept (though I do not think it 

 worth while to discuss) his theory that Venus has a surface shining 

 with metallic lustre, and is surrounded by a glassy atmosphere ; though 

 in that case, again, his descrijition of what he saw may be accepted 

 as it stands, and all that we need reject is his interpretation thereof. 

 In the case of Jupiter's white spots, Mr. Brett's skill as an artist ena- 

 bles us to accept not only his observations, but his interpretation of 

 them, simply because the interpretation depends on artistic, not on 

 scientific, considerations. 



" I wish," he says, " to call attention to a particular feature of Ju- 

 piter's disk, which" (the feature, probably) " appears to me very well 



1 Webb thus describes the egg-shaped clouds : " Occasionally the belts throw out 

 dusky loops or festoons, whose elliptical interiors, arranged lengthways and sometimes 

 with great regularity, have the aspect of a girdle of luminous, egg-shaped clouds sur- 

 rounding the globe. These oval forms, which were very conspicuous in the equatorial 

 zone (as the interval of the belts may be termed) in 1 869-' 70, have been seen in other 

 regions of the planet, and arc probably of frequent occurrence. The earliest distinct 

 representation of them that I know of is by Dawes, March 8, 1851, but they are perhap? 

 indicated in drawings of the last century." 



