198 THE, ANTARCTIC MANUAL. 
(2) Rate of Movement.—Some measure of the snowfall from a 
given area may be obtained by estimating the discharge of ice by the 
glaciers therefrom. For this purpose the rates of flow of the glaciers 
must be measured. 
It is at any rate essential that the average daily rate of flow 
should be determined for several typical ‘Chinese Wall’ glaciers, and 
for a typical ‘snouted’ glacier. 
(3) Nature of Glacier Movement.—That glaciers flow like rivers 
was discovered long ago, but the cause and mode of this movement 
is still an open question. Many theories have been proposed in 
explanation of this, the most important of which are founded, directly 
or indirectly, on a study of the minute structure of glacier ice. All 
ice is composed of an ageregate of irregular crystalline grains, but the 
mode of aggregation of these grains differs materially in different 
kinds of ice. That of glaciers has been found to exhibit a structure 
more or less irregular, and sufficiently coarse to be visible to the 
naked eye, but further information is needed to determine its history 
and significance. The size, shape and optical arrangement of the 
glacier grains should therefore be carefully studied. 
Information is especially wanted as to the crystallographic 
arrangement of the grains in the immediate neighbourhood of the 
shearing planes which are found in Arctic glaciers; especial note 
should be taken whether all the ice grains have their crystallographic 
axes parallel on both sides of such planes, 
The study of the behaviour of the ice along these shearing planes 
is of great interest. If possible, any differences in the rates of move- 
ment on either side of a shearing plane should be measured. The 
changes that occur in the ice may be noted by taking successive photo- 
graphs, at intervals of say a week, of one patch on a glacier face. 
Further a block, including a shear plane, should be cut out of the 
glacier, and the power necessary to deform it, by pressure applied in 
different directions, should be determined. 
(4) The Growth of Glacier Grains.—Attention should be directed 
to the growth of ice grains under strain. Notice whether one grain 
grows by the melting and absorption of surrounding grains, ot 
whether cases occur in which all grains grow simultaneously by the 
introduction of water from elsewhere. 
(5) Internal Melting of Glacier Ice—The extent to which melting 
takes place in glaciers has been again made a matter of primary 
importance by von Drygalski’s work in Greenland. His conclusions 
having been called in question, further data on this point are desired. 
