242 DISCUSSIONS IN CLIMATOLOGY. 



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 doubtless be regarded as somewhat 

 extravagant ; but a slight consideration 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 imagina- 

 tion 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 superficial area. We can realise 

 with tolerable accuracy a thickness of a few miles, but 

 we cannot do this in reference to a superficial area 

 2800 miles across. Consequently, in judging what 

 proportion the thickness of the sheet should bear to 

 the superficial area, we are apt to fall into the error of 



