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POPULAR SCIENCE REVIEW. 
polar and equatorial diameters amounts only to twenty-six 
miles ; these quantities being respectively 7,899 and 7,905 
miles. 
Be the planet circular or elliptical in figure, however, it is 
easy to see that it rotates on its axis, and that too in about the 
same time as Mercury, Venus, and the Earth. In other respects, 
also, the similarity is striking, these planets being nearly of the 
same size, globular figure and density, and differing greatly 
from the huge exterior planets in those respects. The rotation 
of Mars is readily perceived by watching it from hour to hour 
throughout the evening, when it will be seen that the dark 
spots pass over the disc from west to east in the same sense in 
which the Earth is rotating. In about twenty-four hours and 
thirty-seven minutes, or on the following evening, the spot 
which was first observed will be found to have returned exactly 
to the same position, and the others will follow in the same 
succession as on the previous day, the polar snow-spot retain- 
ing nearly the same place. By further watching, the patient 
observer will find that the equator of Mars is only inclined 
a few degrees more to the plane of its orbit than that of 
the Earth, and that, consequently, their seasons are about the 
same. From the longer year of Mars, however, the interval 
during which the polar regions are hidden from and exposed to 
the rays of the Sun, is very different. At the latitude of the 
British islands, the shortest day on Mars is only about six 
hours, whilst on the Earth it is between seven and eight. The 
longest day on Mars, at the same latitude, would be nineteen 
hours, whilst on the Earth it is only seventeen hours. At 
seventy degrees of north latitude the Sun remains above the 
horizon for sixty-nine days, whilst on Mars at the same latitude 
it is above the horizon for 169 days. The pole of Mars is 
exposed to the Sun for 338 days, and hidden from it for the 
same time ; whilst on the Earth the polar day or night is only 
180 days. 
Some observers have complained of the striking monotony 
and uniformity of the surface of Mars. If we cast a glance at 
the accompanying pictures of the planet, we shall hardly be 
disposed to indorse this opinion. On the contrary, the variety 
of scenery is deeply interesting. The seas, or dark portions, 
are remarkably sinuous in their course ; the indentation of the 
coast, caused by bays and creeks, is very picturesque. It is 
true that mountains and vales, such as those on the arid surface 
of the Moon, cannot be perceived ; but by attentive watching, it 
will be seen that the bright portion of the planet is curiously 
dotted over with a mottled ground, and that the dark seas vary 
greatly in the intensity of their tint, even when the spot is at 
the centre of the planet, and is viewed most favourably. It 
