The belts, spots and irregular markings on Jupiter have now been assiduously studied during nearly three centuries. These markings are extremely variable in their tones, tints and relative velocities, and there is little reason to doubt that they are atmospheric formations floating above the surface of the planet in a series of different currents. Certain of the markings appear to be fairly durable, though their rates of motion exhibit considerable anomalies and prove that they must be quite detached from the actual sphere of Jupiter. At various times determinations of the rotation period were made as follows:-- _Date._ _Observer._ _Period._ _Place of Spot._ 1672 J. D. Cassini 9 h. 55 m. 50 s. Lat. 16° S. 1692 " 9 h. 50 m. Equator. 1708 J. P. Maraldi 9 h. 55 m. 48 s. S. tropical zone 1773 J. Sylvabelle 9 h. 56 m. " " 1788 J. H. Schröter 9 h. 55 m. 33.6 s. Lat. 12° N. 1788 " 9 h. 55 m. 17.6 s. Lat. 20° S. 1835 J. H. Mädler 9 h. 55 m. 26.5 s. Lat. 5° N. 1835 G. B. Airy 9 h. 55 m. 21.3 s. N. tropical zone. A great number of Jovian features have been traced in more recent years and their rotation periods ascertained. According to the researches of Stanley Williams the rates of motion for different latitudes of the planet are approximately as under:-- _Latitude._ _Rotation Period._ +85° to +28° 9 h. 55 m. 37.5 s. +28° to +24° 9 h. 54½ m. to 9 h. 56½ m. +24° to +20° 9 h. 48 m. to 9 h. 49½ m. +20° to +10° 9 h. 55 m. 33.9 s. +10° to -12° 9 h. 50 m. 20 s. -12° to -18° 9 h. 55 m. 40 s. -18° to -37° 9 h. 55 m. 18.1 s. -37° to -55° 9 h. 55 m. 5 s. W. F. Denning gives the following relative periods for the years 1898 to 1905:-- _Latitude._ _Rotation Period._ N.N. temperate 9 h. 55 m. 41.5 s. N. temperate 9 h. 55 m. 53.8 s. N. tropical 9 h. 55 m. 30 s. Equatorial 9 h. 50 m. 27 s. S. temperate 9 h. 55 m. 19.5 s. S.S. temperate 9 h. 55 m. 7 s. [Illustration: FIG. 1.--Inverted disk of Jupiter, showing the different currents and their rates of rotation.]