24 
Thickness of the Antarctic Ice , and its [January, 
place in the ice on the inner or poleward side. As such an 
expansive force is assumed to adt in every portion of the 
mass, it follows that the nearer the outside of the sheet the 
more rapidly will the ice move, and consequently the thin- 
ner will the sheet become. 
The Greater 1 hickness of the Sheet at the Pole independent of 
the amount of Snowfall at that place. — It has been proved that 
unless the Antarctic ice were thickest at the pole and thin- 
nest at the edge, motion could not take place. It follows, 
therefore, that however much the snowfall at the edge and 
other places may exceed that at the Pole, or centre of dis- 
persion, the ice must always be thickest at the centre. For 
however small may be the snowfall, and consequent amount 
of ice formed annually at the Pole, snow and ice must of 
necessity continue to accumulate year by year till the sheet 
becomes thickest there. The ice at the Pole could not 
move out of its position till this were the case. Supposing 
there were no snow whatever falling at the Pole, and no ice 
being formed there, still the sheet would be thicker there 
than at the edge. For in this case the ice forming at some 
distance from the pole all around would flow back towards 
the centre, and continue to accumulate there till the resist- 
ance to the inward flow became greater than the resistance 
to the outward ; but this state would not be reached till the 
ice became thickest on the poleward side. 
We have no reason to believe, however, that the quantity of 
snow falling at the Pole is not great. “ One thing we 
know,” says Sir Wyville Thomson, “ that the precipitation 
throughout the Antardfic area is very great, and that it is 
always in the form of snow.” Lieut. Wilkes, of the American 
Exploring Expedition, estimated the snowfall to be 30 feet 
per annum, and Sir James Ross says that during a whole 
month they had only three days free from snow. The very 
fadt that perpetual snow is found at the sea-level at lat. 64° S. 
proves that the amount of precipitation in the form of snow 
in those regions must be great. 
But there is one circumstance which must tend to make 
the snowfall near the Pole great, and that is the inflow 
of moist winds in all diredlions towards it ; and as the 
area on which these currents deposit their snow becomes 
less and less as the Pole is reached, this must, to a cor- 
responding extent, increase the quantity of snow falling 
on a given area. Let us assume, for example, that the 
clouds in passing from lat. 6o° to lat. 8o° deposit moisture 
sufficient to produce, say, 30 feet of snow per annum, and 
supposing that by the time they reach lat. 8o° they are in 
