On the left-hand side of the plain is seen the half-demolished crater Hippalus resembling a large bay, which has its interior strewn with peaks and mountains. On this same side can be seen one of the most important systems of clefts and fractures visible on the Moon, these clefts varying in length from 150 to 200 miles. _Approximate scale, 15 miles--1 inch._ PLATE VII.--PARTIAL ECLIPSE OF THE MOON. _Observed October_ 24, 1874. A view of the Moon partially obscured by the Earth's shadow, whose outline gives ocular proof of the earth's rotundity of form. The shadowed part of the Moon's surface is rendered visible by the diffused sun-light refracted upon it from the earth's atmosphere. Its reddish brown color is due to the absorption, by vapors present near the earth's surface, of a considerable part of this dim light. On both the obscured and illuminated tracts the configurations of the Moon's surface are seen as with the naked eye. The craters appear as distinct patches of lighter color, and the noticeably darker areas are the depressed plains or _Maria_. The large crater _Tycho_, at the lower part of the disk, is the most prominent of these objects, with its extensive system of _radiating streaks_. The largest crater above is _Copernicus_, at the left of which is _Kepler_ and still above are _Aristarchus_ and _Herodotus_ appearing as if blended in one. Above and at the left of the great crater _Tycho_, the first dark tract is the _Mare Humorum_ of Plate VI., seen in its natural position, with the crater _Gassendi_ at its northern (upper) extremity and _Vitello_ on its southern (lower) border. The advancing border of the shadow appears, as always, noticeably darker than the remainder, an effect probably of contrast. The illuminated segment of the Moon's disk has its usual appearance, the lighter portions being the more elevated mountainous surfaces, and the dark spaces the floors of extensive plains. _Approximate scale, 140 miles--1 inch._ PLATE VIII.--THE PLANET MARS. _Observed September_ 3, 1877, _at 11h. 55m. P. M._ A view of the southern hemisphere of Mars, when in the most favorable position for observation, and when exceptionally free from the clouds, which very frequently hide its surface configurations. Since, of all the planets, Mars is most like the earth, Plate VIII. may give a fair idea of the appearance of our globe to a supposed observer on Mars. The dark gray and black markings, are regarded as tracts of water, or of some liquid with similar powers of absorbing light; and, for the same reason, the lighter portions, of a prevailing reddish tint, are supposed to be bodies of land, while the bright white portions are variously due to clouds, to polar snow or ice, and the bright rim of white along the limb, to the depth of the atmosphere through which the limb is seen. The chief permanent features of the planet's surface have been named in honor of various astronomers.