It should be mentioned here that the above times of rotation are derived from atmospheric features more or less volatile in nature, and that therefore the actual sphere of Jupiter rotates in a period which we have not precisely discovered. No doubt the motion of the real surface is not very different from that of the atmospheric markings above it. There is reason to think that, whatever the character of the planet’s crust may be, we have never yet obtained a glimpse of it. A dense veil of impenetrable vapours appears to surround the globe on all sides, and this is subject to violent derangement from the evolution of heated material or gaseous fluids from the surface below. These disturbances seem to be very durable in some instances as to their observed effects. The atmosphere would, in fact, appear to possess a singular capacity for retaining the impressions of its changes. The permanency of certain spots can hardly be due to continued action from those parts of the disk immediately underlying them; for their variable motions soon transport them far from the places at which they were first seen, and prove their existence to be quite independent of their longitude. _Nature of the Red Spot._—There is much in connection with the red spot that remains in mystery. Its dimensions, form, and motion have severally been ascertained within small limits of error, and the alterations in its tint and degree of visibility have been recorded with every care. But we can only conjecture as to the origin, character, and end of this remarkable formation. What agency produced it, and moulded the definite elliptical outline it has always preserved—what forces control its oscillations of speed, and keep it suspended so long in the aerial envelope of Jupiter—are matters of pure theory. When, in July 1878, it first came under notice it was a well-developed object, and though Russell in 1876, Lord Rosse and others in 1873, and Gledhill and Mayer in 1869-70 had delineated forms suspiciously like the red spot and situated in the same latitude, yet the several features may not have been absolutely identical, for nothing was seen of the spot in 1877 or in some other years. But there is a strong probability that the red ellipse of 1869-70 must have been the red spot in an incipient stage of its formation. The object may have undergone temporary obscuration, similarly to Cassini’s spot two centuries ago. [Illustration: Fig. 33. I. 1857, Nov. 27. (Dawes.) | II. 1859, Dec. 29. (Huggins.) III. 1858, Mar. 2. (Huggins.) | IV. 1870, Jan. 23. (Gledhill.) V. 1872, Feb. 2. (Gledhill.) | VI. 1885, Feb. 25. (Denning.) ]