2. There is an intricate mass of surface-markings on the planet, which, in its main features, is capable of being satisfactorily delineated, and which in its general aspect is similar to the canals depicted by Schiaparelli, though not nearly so pronounced, straight, and uniform as he has shown in his charts. 3. The detail is visible in the form of irregular streaks, condensations, and veins of shading, very faint and delicate in some parts. The veins apparently connect many of the larger spots, and here and there show condensations, which have sometimes been drawn as isolated spots. A night of good definition, however, reveals the feeble ligaments of shade connecting them. 4. That there exists on the immediate borders of many of the darker patches and veins a remarkable brightness or shimmering, which reminds one of the bright spots merging out of the dark belts on Jupiter. Just contiguous to the “Kaiser Sea,” and on its eastern limits, this brightness was so striking in March 1886 as to compare with that exhibited by the N. polar cap. In drawings by many observers these regions of special luminosity have no place, but there is little doubt they occupy a leading position in the physical configuration of Mars. 5. That there is no trace of a dense atmosphere on Mars, as some of the text-books infer. The pronounced aspect of the chief markings, their durableness and continuity of form, the ease with which they may be traced up to the limb, the absence of phenomena indicating dense cloud-bearing air-strata, and other observed facts verify the conclusion that the planet’s surface is comparatively free of vapours, and in a totally different condition to that of Jupiter and Saturn. _Rotation of Mars._—The diurnal period of this planet is known with far greater certainty and precision than that of any other planet, the Earth excepted. It will be useful to quote the values derived since Cassini’s time:— h m s 1666. J. D. Cassini 24 40 1704. J. P. Maraldi 24 39 1781. W. Herschel 24 39 21·7[31] 1784. W. Herschel 24 37 27 1838. J.H. Mädler 24 37 23·8 1845. O. M. Mitchell 24 37 20·6 1859. A. Secchi 24 37 35 1864. F. Kaiser 24 37 22·62 1866. R. Wolf 24 37 22·9 1869. R. A. Proctor 24 37 22·735 1873. F. Kaiser 24 37 22·591 1873. J. F. J. Schmidt 24 37 22·57 1883. A. Marth 24 37 22·626 1884. W. F. Denning 24 37 22·34[32] 1885. H. G. v. de S. Bakhuyzen 24 37 22·66 The last of these, by Prof. Bakhuyzen of Leyden, is probably the best. It was based on a large number of observations extending over 220 years, viz. from those of Huygens in 1659 to those of Schiaparelli in 1879.