74

THE ALPINE REGIONS.

Although several theories have heen advanced to explainthe cause of glacier motion, three especially have attractedattention. The first of these, in point of time, was advancedhy Scheuchzer in 1705, and developed hy M. de Charpentier.The idea is as follows: that the whole mass of the glacier istraversed by a number of exceedingly minute fissures or veins;that these are filled from time to time with water, producedhy the ice thawing under the influence of heat or pressure,which, owing to some change in the external circumstances, isagain frozen. Water, it is well known, expands when it isconverted into ice: hence the freezing of a quantity of water,dispersed throughout the body of the glacier, would, if it wereunconstrained, cause expansion in all directions. In the casehowever of a glacier on a mountain side, motion takes place inthe only unopposed direction, that is, downwards. To thistheory there are many grave objections: it does not satisfac-torily explain several of the peculiarities of glacier motion, suchas its resemblance to that of a river, and the fact that it iscontinued even during the coldest winters, and is not liable toany marked change when there is a sudden alteration in thetemperature of the surrounding air. The advocates, moreover,of this theory have failed to prove the existence of these fineveins or capillaries, as they are commonly called. No doubt,near the surface of a glacier, the ice is often ill compacted, andreadily breaks asunder, but this is only because, like river ice,it has become ‘rotten’ through exposure to the air. In thebody of the glacier no such tendency to separation can bedetected. Dr Tyndall' and Mr Huxley made a number ofexperiments on the Mer de Glace and its tributaries, and wereunable to find any proof of their existence in sound un-weathered ice. Holes were bored carefully in the ice, and filledwith coloured liquids, but these did not in any way diffusethemselves in the surrounding ice. Dr Tyndall says ‘I have

1 Glaciers of the Alps , p. 338.