ICE OBSERVATIONS. 199 
If glaciers move by the continual melting and re-freezing of the ice 
grains, then temperatures at which this can occur should be met with 
in glaciers. A platinum thermometer is the most suitable instrument 
to determine the temperature in the body of a glacier, but mercurial 
thermometers, buried at various depths, can also be used. A consider- 
able series of observations should be undertaken to determine (1) the 
rate at which heat waves traverse the ice; (2) the depth affected by 
superficial changes of temperature; (3) the minimum temperature 
to be found in the lower part of a glacier. 
(6) Ablation—The extent to which the upper layers of a glacier 
are removed by melting and evaporation—known as ablation—must 
be systematically measured by driving graduated sticks into the ice. 
In connection with ablation, it is advisable to determine the loss 
in weight of an exposed block of ice. In comparison with this experi- 
ment, similar measurements should be made as to the rate of solution 
of ice exposed in the sea at temperatures below the freezing-point of 
fresh water. 
(7) Thickness of the Antaretie Ice-Shect—Estimates of the thick- 
ness of the Antarctic ice-sheet will be difficult to form. The only 
means of forming an approximate estimate may be by transverse 
sections facross the country, showing the surface slope of the ice in 
reference to any rock-peaks that rise above it. The view that the ice 
will steadily increase in thickness to the South Pole, where it may 
amount to 20 miles, is apparently hypothetical, and not easy to 
reconcile with the known properties of ice. 
(8) Glacial Uplift—The fate of water produced by ablation 
should be traced if possible. The water, for instance, may percolate 
to low levels in the ice-mass and there be again frozen. In that case 
the layers of a glacier may be subject to a gradual uplift, due to the 
removal of the top layer and its transference by percolation and 
re-freezing to the bottom. 
The uprise of the lower layers of a glacier has been assumed by 
some geologists to explain certain features of European glacial de- 
posits, and it has been observed to occur on the margins of Arctic 
glaciers in Greenland and Spitzbergen. 
To what extent material from the bed of the glacier is uplifted by 
such a movement should be carefully investigated. It is also possible 
that in some cases the ice-mass may be forced up hill by the pressure 
of that which is descending from a higher level, or in other words that 
a glacier may behave somewhat in the way of water at the foot of a 
steep, slope. All proofs that any such thing has occurred should be 
