266 W. J. McGee—Thickness of Ice-sheet at any Latitude. 
area of zone bounded by margin of ice, and n area of hemis- 
phere. Table XVIII has been computed in accordance with 
this ratio. 
TABLE XVIII. 
Maximum thickness of Ice-cap. 
Thickness of Ice-cap. 
Temper- . Value of 
Latitude. Stare. Bh ay p22. Miles. 
10° +179°9° FB. 1°020 in. 1°863 55,871 10°582 
20 1-4 “940 71-559 46,753 8°855 
30 69°8 728 17092 32,749 67203 
40 56°5 457 “620 18,594 3°422 
50 41°7 264 *326 Ba Bg 4 1°852 
60 30°2 168 “yok 5,728 1:085 
70 16°0 090 "095 2,80 530 
80 6°8 059 “060 1,799 341 
90 23 048 “048 1,440 273 
It is almost needless to reiterate the proposition already de- 
monstrated, that vapor could not be borne far enough within 
the margin of the ice to affect materially the above results, with- 
out seriously deranging the sequence of phenomena to which 
the ice owes its origin and conservation. 
he suggestion that the property of flowing might enable 
the ice to assume a uniform depth may be anticipated by men- 
tioning that the polar slope above given is less than one-tenth 
of that requisite, according to Hopkins’s experiments, to pro- 
duce the slightest motion. 
2. COMPARISON WITH THE ICE-CAP THEORY. 
alone. net Be found that ice barely moves on a slope of one 
ir ille Thompson says: “It seems now to be thoroughly established by 
lines of trustworthy soundings which have been run in all directions, that the 
average depth of the ocean is a little over 2,000 fathoms.” This Journal, vol. 
xvi, (1878), p. 351, Dr. Kriimmel estimates the mean depth at 1877 fathoms. 
See note in Popular Science Monthly, vol. xvi, Dec, 1879, p. 287. 
