PRESSURE OF TIDAL GLACIERS 
211 
CL 
2,000 feet to 1,400 feet (c). This is equivalent, so far as 
the block of ice is concerned, to raising the sea bottom 
from its position in a until it touches the base of the ice¬ 
berg. The ice is not lifted by the sea bottom; it still pro¬ 
jects into the air just 200 feet; it is still supported by the 
water, and though touching the sea bottom does not press 
on it. Finally, conceive the water drawn down until its 
depth is but 700 feet (d). This depth of water is just 
able to float a berg 800 feet thick. Therefore 800 feet of 
ice, or one-half the thickness of the block, are now sup¬ 
ported by the water, and the remaining 800 feet by the 
sea bottom. 
Let us now approach the subject in a different way. 
Begin with a block of ice of the same dimensions as be¬ 
fore, resting on a horizontal bed, with which it is every¬ 
where in contact (fig. 104, a). The pressure on each square 
inch of the bed equals the weight of the 
column of ice above it—about 640 
pounds. Now introduce sea water about 
the ice until it has a depth of, say, 700 
feet (&). The water presses horizontally 
against the vertical faces (as indicated by 
the arrows), but, as there is no vertical 
component to a horizontal force, the water 
pressure neither lifts the ice block nor 
pushes it down. The block continues 
to rest on the bed, exerting still a downward pressure of 
640 pounds per square inch of base. This line of reason¬ 
ing seems quite as plausible as the other, but the result 
is different. 
A little consideration discovers the cause of the dis¬ 
crepancy. In the first analysis it is tacitly assumed that 
the water exerts its pressure not only on the sides of the 
ice block but on its base, and this whether the block floats 
free or touches the sea bed. In the second analysis it is 
FIG. IO 4 . DIAGRAMS 
ILLUSTRATING NON¬ 
FLOTATION THEORY 
OF TIDAL GLACIERS. 
