176 The American Geologist. March, looi. 
our own at sea level, it may render as effective a covering as 
our own. While not affirming that this is the case, he notes 
simply "how little we need go out of our way in possibilities 
to furnish Mars with a sufficient covering." 
After sufficiently showing that these phenomena on Mars 
are due to ice and snow about the poles, and to the produc- 
tion of water as the caps recede, Mr. Lowell notes some pe- 
culiarities by which they dift'er from the snow caps of the earth. 
In many respects they are comparable and similar, but ours 
have greater extension, reaching, in the northern hemisphere, 
in their maximum, southward to about the latitude of 45°, pro- 
ducing a snow-spot about 90° in diameter. It would thus ap- 
pear to an outside observer. "In this we live and move and 
have our being for some four months, and it is at least a preg- 
nant thought that to such an outsider the highest development 
of life upon our planet should seem thus for nearly half the 
year to have its existence within the polar cap." From this 
maximum our snow cap, as viewed from Mars, would appear 
to dwindle till, about two months after the summer solstice, 
it would measure only about 40° across. The southern cap, 
from incomplete data, seems to be larger than the northern, 
both at maximum and at minimum. 
On Mars the northern snow cap has a maximum of yo\ 
about 53 of its own days after winter solstice. It recedes then 
to a minimum of 3° which occurs about the same time after the 
summer solstice, and it retains the minimum size some time. 
Comparing therefore the northern caps of the two planets, it is 
apparent that that of the earth is greater than that of Mars at 
each extreme. As to the maximum this happens in spite of the 
fact that the Martian year and therefore the Martian winter is 
nearly twice as long as our own. 
Again the ratio between the maxima and minima on the 
earth are as five to one, while on Mars they are as 130 to one. 
"To the belief that Mars lacks warmth this comparison is cal- 
culated to give a shock of surprise." 
A still more remarkable contrast exists. This is the differ- 
ence in behavior of the two Martian caps. The southern cap 
is bigger than the northern in winter and smaller in summer. 
It surpasses it in accumulation and again in dissipation. This 
can be affirmed, although the data of observation on the 
northern maxima are not satisfactorv. 
