Page:Popular Science Monthly Volume 1.djvu/306

294 inexplicable (as it seems to us) if the sun occasions all these meteorological changes in Jupiter, as he occasions all the changes which take place in our earth's atmosphere. The alternation of day and night, which is one of the most potent of all the circumstances affecting the earth's meteorological condition, appears to have no effect whatever on the condition of Jupiter's atmosphere!

Now, as respects the alternation of summer and winter, we can form no satisfactory opinion in Jupiter's case, because he has no seasons worth mentioning. For instance, in latitudes on Jupiter corresponding to our own, the difference between extreme winter and extreme summer corresponds to the difference between the warmth on March 12th and March 28th, or between the warmth on September 15th and on September 30th. Yet we are not without evidence as to seasonal meteorological effects in the case of the sun's outer family of planets.. Saturn, a belted planet like Jupiter, and in all other respects resembling him, so far as a telescopic study can be trusted, has seasons even more markedly contrasted than those on our own earth. We see now one pole now another bowed toward us, and his equatorial zone is curved now downward now upward, so as to form two half ovals (at these opposite seasons), which, taken together, would make an ellipse about half as broad as it is long. As no less than fourteen years and a half separate the Saturnian summer and winter, we might fairly expect that the sun's action would have time to exert itself. In particular, we might fairly expect the great equatorial zone to be displaced; for our terrestrial zone of calms or "doldrums" travels north and south of the equator as the sun shifts northward and southward of the celestial equator, accomplishing in this way a range of no less than three thousand miles. But the Saturnian equatorial zone is not displaced at all during the long Saturnian year. It remains always persistently equatorial! Nothing could be more easy than the detection of its change of place if it followed the sun; yet no observer has ever suspected the slightest degree of systematic change corresponding with the changes of the Saturnian seasons. Or, rather, it is absolutely certain that no such change takes place.

It appears, then, that night and day, and summer and winter, are alike without influence on the Jovian and Saturnian cloud-zones. Can it reasonably be questioned that, this being the case, we must look for the origin of the cloud-zones in these planets themselves, and not in the solar orb, whose action must needs be largely influenced by the alternation of night and day and of the seasons?

But further, we find that a circumstance which had seemed perplexing, when we compared the Jovian belts with terrestrial trade-wind zones, finds an explanation at once when we regard the belts as due to some form of action exerted by the planet itself. For, let us suppose that streams of vapor are poured upward to vast heights and with great velocity from the true surface of the planet. Then such streams,