In periods of calm, very few changes are noticeable in the markings of the planet, except, perhaps, some slight modifications of form in the cloudy, equatorial belt which, in general, is much more liable to changes than the other belts. But the Jovian surface is not always so tranquil, great changes being observed during the terrific storms which sometimes occur on this mighty planet, when all becomes disorder and confusion on its usually calm surface; and nothing on the Earth can give us a conception of the velocity with which some of its clouds and spots are animated. New belts quickly form, while old ones disappear. The usual parallelism of the belts no more exists. Huge, white, cumulus-like masses advance and spread out, the rosy equatorial belt enlarges sometimes to two or three times its usual size, and occupies two-thirds, or more, of the disk, the rosy tint spreading out in a very short time. At times very dark bands extending across the disk are transformed into knots or dark spots, which encircle the planet with a belt, as it were, of jet black beads. Sometimes, also, a secondary but narrower rosy belt forms either in the northern or the southern hemisphere, and remains visible for a few days or for years at a time. On May 25, 1876, I witnessed one of the grandest commotions which can be conceived as taking place in an atmosphere. All the southern hemisphere of Jupiter, from equator to pole, was in rapid motion, the belts and spots being transported entirely across the disk, from the eastern to the western limb, in one hour's time, during which the equatorial belt swelled to twice its original breadth, towards the south. Now, when one stops for a moment to think what is signified by that motion of the dark spots across the little telescopic disk of Jupiter in an hour's time, he may arrive at some conception of the magnitude of the Jovian storms, compared with those of our globe. The circumference of Jupiter's equator, as stated above, is 276,460 miles; half this number, or 138,230 miles, represents the length of the equatorial line seen from the Earth. Now, after taking into account the rotation of the planet, which somewhat diminishes the apparent motion, we arrive at the astonishing result that the spots and markings were carried along by this Jovian storm, at the enormous rate of 110,584 miles an hour, or over 30.7 miles a second. On our globe, a hurricane or tornado, which blows at the rate of 100 miles an hour, sweeps everything before it. What, then, must be expected from a velocity over 1,105 times as great? Enormous as this motion may appear, its occurrence cannot be doubted, since it is disclosed by direct observation. The surface of Jupiter, it would seem, has its periods of calm and activity like that of the Sun, although it is not yet known, as it is for the latter, that they recur with approximate regularity.