90 THE ANTARCTIC MANUAL. 
ment than to expose a block of compact blue ice taken from ‘the 
interior of the glacier to the direct rays of a powerful sun. Such a 
block is easily obtained by penetrating into the grotto, from which 
the glacier stream issues, to such a distance that direct sky-light is 
shut out. Any of the blocks found there will do, and it is to be 
brought out and exposed on a rock. In twenty minutes or half an 
hour the block falls down into a heap of irregularly shaped pieces of 
ice, each of which is a grain and a single crystalline individual. In 
higher latitudes or in dull weather, the power of the sun is not 
sufficiently strong to effect this complete and striking dissolution, 
but it loosens the block into its grains, which will rattle if the block 
be shaken. 
The writer has analysed blocks of ice from many Swiss glaciers, 
and weighed the individual grains. They are of all weights up toa 
certain maximum, which varies with the glacier and the part of it 
furnishing the ice. The largest that he met with was from the 
Aletsch glacier, and it weighed 700 grams. It is the size or weight 
of the largest grains that it is important to determine. Small grains 
are abundant in every glacier, and are a necessity in order that the 
larger ones may pack close. The size of the largest grains is what is 
referred to when we read that the grain of this glacier is large or of 
that one small. The shape of the grain is irregular, and no two of 
them are alike, but they fit into each other like a puzzle. They 
resemble a collection of vertebra more than anything else. Indeed, 
if the disarticulated vertebre of an animal, especially one with a 
long tail, were carefully packed into a box of a suitable size, so as 
to occupy the least possible space, the boxful of vertebrz would 
resemble the block of ice which has been loosened by a moderate 
sun, and would rattle, when shaken, in much the same way. If 
gelatine were allowed to run into the box and set, we should have 
a model of the block of ice before exposure to the sun. If the box 
of vertebrae were exposed to the sun, the gelatine would be liquefied, 
and the mass would be loosened as in the case of the ice. What is it 
in the block of ice which corresponds to the gelatine in our ilustra- 
tion with the vertebre? It is the slightly impure water which 
surrounds the grains and in which they float or try to float. Under 
the influence of cold, this impure water supplies pure ice to the grain 
with which it is in contact, while its freezing-point continually falls; 
finally its freezing-point and the temperature to which it is exposed 
reach a minimum, and the grain remains in contact, even in mid- 
winter, with a film of brine, which may be very minute. With 
rising temperature the grain begins to melt at the temperature at 
