48 Chemical and Physical Notes 



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 vertebrae more than 

 anything else. Indeed, if the disarticulated vertebrae 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 vertebrae 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 illustration with the vertebrae ? 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 which it ceased to freeze, it dilutes the brine, 

 and raises its own melting-point. We see, then, that the 

 grain of the glacier may be surrounded in summer by a 

 relatively considerable envelope of water of comparative 

 purity and high freezing-point, while in winter it is sur- 

 rounded by a mere film of brine of comparatively low 

 freezing-point. The greater the amount of solid matter 

 dissolved in the water, or the greater its salinity, the greater 

 is the amount of liquid surrounding the ice-grain at a given 

 temperature. The salinity of the water does not require to 

 be very great for it to furnish, when frozen, an ice which is 



