_Observations of Hooke, Cassini, and others._—Hooke and Cassini were amongst the first to find definite spots on the surface of Jupiter. From 1664 to 1667 a particularly large and distinct spot was frequently seen in the planet’s S. hemisphere. This object disappeared in the latter year, but returned in 1672, and was seen until the close of 1674, when it again temporarily vanished, to reappear at subsequent epochs. Cassini was enabled to determine the rotation-period from this spot. He found that the markings in the immediate vicinity of the equator moved with greater celerity than those in higher latitudes, the difference in their rotation-periods being nearly 6 minutes. A century later Sir W. Herschel confirmed these results: he saw a bright spot which completed a rotation in nearly 5 minutes less time than several dark spots. Schröter also made many observations, and noted frequent changes in the spots and differences in their rotation-periods. He watched a bright object near the equator which had a period more than 5 minutes less than some dark spots. In later years Mädler and others followed up the investigation of these markings, and with nearly similar results. The various spots were undoubtedly affected by proper motions, enabling them to yield discordant rotation-periods. Bright forms near the equator moved with great rapidity and effected a rotation in about 9^h 50^m, while dark spots on either side of it occupied between 9^h 55^m and 9^h 56^m. The markings were evidently controlled by currents of different velocities in the planet’s atmosphere. Dawes, in 1849 and following years, noted luminous spots, like satellites in transit, on a belt in the planet’s S. hemisphere. In October 1857 he observed a group of eleven of these objects; and in 1858 Lassell saw many similar appearances in a bright belt near the equator. _The Ellipse of 1869-70._—In 1869 and 1870 Gledhill, of Halifax, and Prof. Mayer, of the Lehigh University, saw a remarkable formation just south of the great belt lying on the S. side of the equator. It was in the form of a perfect ellipse, ruddy in colour, and very distinct in outline. Its major axis was parallel with the belts. It was first observed on Nov. 14, 1869, and had disappeared in July 1870, though on Dec. 1, 1871, a similar elliptic ring was seen resting on the S. equatoreal dark band. _The Red Spot._—In July 1878 a large spot, of oval form and intense red colour, appeared in about the same latitude as the ellipse seen by Gledhill and Mayer in 1869-70. It was first announced by Dennett of Southampton, though it appears to have been seen a few weeks earlier by Prof. Pritchett, of Missouri, U.S.A. The object alluded to soon attracted general notice; and as it continued visible during the oppositions of 1879, 1880, and 1881 under the same striking aspect, it created a considerable stir among telescopists, and the “great red spot on Jupiter” became familiarly known both in appearance and in title.