Page:Popular Science Monthly Volume 11.djvu/96

86 its turn bringing on a fresh explosion. Now, a rhythmical succession 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 sufficient 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 observer of Jupiter with high telescopic 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 details are examined. It appears to me that considerable interest attaches 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 attention to errors into which, in my judgment, he has fallen. For instance, I certainly do not think he has ever seen the solar corona when the sun was not eclipsed, though I have no doubt he saw what he described, 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 description 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 enables 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 Jupiter's disk, which" (the feature, probably) "appears to me very well