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THE ALPINE REGIONS.

reuniting: and that in a word, although ice when subjected topressure presented analogies with a plastic body, it failed todo so under tension. He also observed that when a sunbeamwas passed through a plate of ice, which had been formedregularly, star-like flowers appeared within the ice, lying inplanes parallel to its surface; shewing thus that the crystalsof which the mass was composed, the courses as it were of itsmasonry, could be detected in taking it to pieces by a processthe reverse of that which had built it up. He applied thesame test to glacier ice, and found that in it no such definiteplanes of freezing could be detected. Sometime before DrTyndall commenced his experiments, Dr Faraday had shewnthat two pieces of ice, if placed in contact with their surfacesmoistened, would always freeze together. This property, then,Dr Tyndall applies to explain the phenomena of glaciers; heconsiders that glacier ice cannot in any sense be called a viscousbody or fluid ; because it has not been proved that it can bestretched in even a slight degree without breaking. Hemaintains therefore that a glacier descends a slope by reasonof its own weight, the pressure of the mass of snow above it,and perhaps the gradual melting of that part of its surfacewhich is in contact with its bed ; that during its descent itis continually being broken by tension, and being healedby regelation, when that tension is removed or replaced bypressure; consequently that, although many of its phenomenaare suggestive of plasticity or viscosity, it cannot in strictnessbe said to be endued with any such property. The questionat issue cannot perhaps as yet be regarded as wholly settled;still Dr Tyndall has certainly proved that ice, if plastic at all,is only so in a very slight degree, and that Professor Forbeswas unfortunate in making use of the term viscous, as beingvery liable to misconception and standing in need of manylimitations.

So much then for the phenomena of glaciers; and now as we