south which are red, green, brown, black and brilliant white. The spots on the equatorial belt move rapidly toward the west with a speed of over 270 miles an hour, with respect to the other markings on the planet. By watching these impressive colorings and markings the gigantic globe may actually be seen to turn around on its axis! It does this in only 9 hours and 50 minutes—less than half the time that it takes the earth to rotate.
With a still larger telescope, however, it was discovered that 9 hours and 50 minutes was only the average time that it takes Jupiter to rotate and that the day varies according to the location on the planet. Thus, like the sun, its surface is not a fixed one, for at the equator the rate of rotation is 9 hours and 47 minutes, a little distance at either side 9 hours and 56 minutes, and in higher latitudes over 10 hours. But Jupiter is not as hot a globe as the sun, which has been described as somewhat resembling "thick molasses," for if it shone by its own light it would not cast a shadow, nor would the shadows of its satellites be dark spots upon its surface.
Such facts have led to the general belief that Jupiter is still in an early stage of development with its globe probably in a semi-fluid condition so hot that the gases which will some day form its waters and be cradled in the hollows of its crust, now rise as hot vapor into its thick, warm atmosphere and fall as incessant rains. The surface visible to us on earth must therefore be in the nature of dense clouds and vapors while its real surface is probably in a "hot, muddy thickish liquid" condition, quite unattractive to think about.
Yet there are some considerations that tend to disprove the cloud theory. Barnard mentions that the semi-permanent nature often shown by the markings is against it. The great Red Spot has been visible at intervals for a hundred years or more, and other markings may be traced with but little change of form for
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