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POPULAR SCIENCE REVIEW. 
northern patch of snow varies hut slightly in dimensions, the 
southern is of great size in the winter, and almost vanishes in 
summer. 
From the foregoing facts, and the deductions which may 
naturally he drawn from them, the reader has ample means for 
judging, in this individual instance at least, as to the probability 
of the planets being the abode of animal and vegetable life. It 
would be impossible, of course, to give any minute details on 
this point, — to say that such a place is forest land, or cultivated 
ground, or artificial formations ; for when Mars is nearest the 
Earth — making use of the most powerful telescope yet con- 
structed, — the observer is merely able to tell whether a space 
of ground which is two hundred miles long by two hundred 
broad, or an area of 40,000 miles, is round or square. From 
this circumstance, the observations of Schroeter, who saw clouds 
passing over the planet with a velocity from forty to sixty 
times that of the most violent hurricanes on the Earth, have 
been much doubted. But otherwise we have every evidence of 
an atmosphere, of snow, of changeable weather, of bright and 
sunny skies, of the existence of water. The seasons, though 
not so equable in duration as those on the Earth, are still pre- 
sent, with all then agreeable changes ; we see the seed-time and 
harvest, the ripening summer and the dark winter. The iso- 
thermal hues on the Earth are reproduced on Mars, if we are 
to judge by the position of the snow-zones, which are not placed 
exactly at the poles. Nor does the excessive cold which might 
be surmised to take place from the planet’s distance from the 
solar heat really appear to be so severe. Whether, from some 
peculiarity in the atmosphere, the latent heat of the body itself, 
or other causes unknown to us, the polar snows do not appear 
of the vast extent which might be imagined. Even those thaw 
away with a rapidity which seems marvellous, whilst the equa- 
torial regions are altogether free from such visitations. Venus 
receives four times the heat of Mars, and twice that of the 
Earth; yet at the North Pole of Venus, a bright white and 
large spot has been perceived, which may naturally be surmised 
to be of the same nature as the snow-capped poles of the Earth 
and Mars ; and we might from this conclude that no great 
difference exists in those three planets at least, whatever may 
be the case in the other two groups of planets, — i.e., the seventy- 
six asteroids, or the huge exterior planets of small density, quick 
rotation, and accompanied by numerous moons and a ring. 
The diameter of Mars is about twice that of the Moon, and 
more than one-half of that of the Earth. Its surface is about 
four times greater than that of the former, and is one quarter 
that of the latter. Bulk for bulk, Mars is seven times larger 
than the Moon, and the Earth is seven times larger than Mars. 
