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Thickness of the Antarctic Ice , and its [January, 
4. The area of the sheet, the thickness of its edge, the 
velocity of its motion outwards, the amount of snow- 
fall, and the temperature of the climate are so related 
to one another that the value of any one of them can 
be determined approximately in terms of the rest. 
The probable Thickness of the Ice at the Pole. — The point 
which now remains to be determined is, What is the thick- 
ness of the ice at the Pole, or centre of dispersion ? The 
thickness of the sheet at the edge is admitted to be about 
1400 feet, and this, as has been demonstrated, must be the 
thinnest part of the sheet. It must gradually thicken inwards 
towards the Pole as centre of dispersion, where the thickness 
becomes a maximum. How much thicker, then, must the 
sheet be at the centre than it is at the circumference ? The 
question to be determined, stated in another form, is, What 
is the thickness of ice at the Pole required in order to impel 
the cap outwards in all directions at the rate of a quarter of 
a mile per annum, or even half that rate per annum ? The 
upper surface of the sheet must slope upwards towards the 
centre or pole. What is the amount of this slope ? 
The Antarctic continent is generally believed to extend on 
an average from the South Pole down to about, lat. 70° or 
so. In round numbers we may take the diameter of the 
continent at 2800 miles. The distance from the edge of the 
ice-cap to its centre, the Pole, will therefore be 1400 miles. 
A slope of 1 degree, continued for 1400 miles, will give 
24 miles as the thickness of the ice at the Pole. But would 
a slope of 1 degree be sufficient to produce the required 
amount of motion ? If the generally accepted theory of the 
cause of glacier motion be correct, it certainly would not. 
But supposing we assume that one-half or even one-quarter 
that amount of slope would suffice, still we have 6 miles as 
the thickness of the cap at the Pole. 
To those who have not been accustomed to reflect on the 
physical conditions of this problem, this estimate may doubt- 
less be regarded as somewhat extravagant ; but a slight con- 
sideration will show that it would be even more extravagant 
to assume that a slope of less than half a degree would be 
sufficient to produce the necessary outflow of the ice. In 
estimating the thickness of a sheet of continental ice of one 
or two thousand miles across, our imagination is apt to 
deceive us. We can easily form a pretty accurate sensuous 
representation of the thickness of the sheet, but we can 
picture to ourselves no adequate representation of its super- 
ficial area. We can realise with tolerable accuracy a thick- 
