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seen floating above the surface of the Polar seas, form only 
small portions of the actual icebergs. 
The specific gravity of ice at 0° C. is 0*9175, the specific 
gravity of sea water at the same temperature 1'029. Hence 
the volume of ice below the water is 8*2169 times that above. 
Next, as to the resistance ofiered by ice to crushing and 
extension. In experiments made by Canon Moseley, a rod 
of ice 12 inches long and IJ inches diameter was firmly 
clamped at the top and gradually weighted at the bottom 
till the ice gave way, the rod of ice being vertical. The re- 
sults vary from 70 to 116 lbs. per square inch; the ice was 
in a melting condition. 
The tenacity of other materials expressed in the same 
way is for brick, 280 to 300 lbs. ; lead, 3,300 lbs.; oak, 
10,000 lbs. ; cast-iron, 16,000 lbs.; wrought-iron, 51,000 lbs. ; 
and steel, 130,000 lbs. 
Canon Moseley also determined the pressure necessary to 
crush ice directly, and found that an inch cube of ice bore 
308 lbs., and then gave way. This is about the same as for 
chalk, the weight necessary to crush chalk being 330 lbs. 
per square inch ; for brick, 1,000 lbs. ; for marble, 5,500 lbs ; 
and cast-iron, 112,000 lbs. 
An easy calculation shows that the height of a column 
of ice which would just crush at the base by its own weight 
is 748 ft. The force necessary to shear ice has been found 
by Canon Moseley to be 118 lbs. per square inch. Yet this 
substance which crushes more easily than chalk, and tears 
asunder almost more easily than any other substance, is 
found in huge masses descending irregular valleys of gentle 
slope, apparently by its own weight, moulding itself like a 
plastic substance to the form of its channel, flowing here 
more quickly, here more slowly, in the very same way that 
water would flow down the same channel, though, of course, 
at a much slower rate. The explanation of this remarkable 
