It is unnecessary for us to explain why this answer was unsatisfactory. Subsequent observations, however, proved its impossibility, and Professor Forbes then put forward his ideas of the _viscous character_ of ice. But these, too, did not meet the conditions of the phenomenon; and the view now adopted is that of Professor Tyndall, who has shown that it is the result of the regelation we have already described. Professor Forbes enunciated his theory in words to the following effect: “A glacier is an imperfect fluid or viscous body, which is urged down slopes of certain inclination by the natural pressure of its parts.” But we know the exceeding brittleness of ice, and how is viscosity compatible with brittleness? We know, too, that crevasses and fissures will suddenly form on a glacier, like the cracks on a pane of glass. But if ice were viscous, and could expand, dilate, or stretch as viscous substances do, these crevasses would be impossible. They would gradually close up, like an indent in a mass of jelly. And yet it cannot be denied that a glacier _does_ move like a viscous body; the centre flowing past the sides, the top flowing over the bottom, while the motion through a curved valley corresponds to fluid motion. How are we to reconcile these apparently conflicting circumstances? By Professor Tyndall’s regelation theory, which is founded on a fact already mentioned; namely, that when two pieces of thawing ice are brought in contact, they freeze together. This _fact_, and its application irrespective of the _cause_ of regelation, may be thus illustrated: “Saw two slabs from a block of ice, and bring their flat surfaces into contact; they immediately freeze together. Two plates of ice, laid one upon the other, with flannel round them overnight, are sometimes so firmly frozen in the morning that they will rather break elsewhere than along their surface of junction. If you enter one of the dripping ice-caves of Switzerland, you have only to press for a moment a slab of ice against the roof of the cave to cause it to freeze there and stick to the roof. “Place a number of fragments of ice in a basin of water, and cause them to touch each other; they freeze together where they touch. You can form a chain of such fragments; and then, by taking hold of one end of the chain, you can draw the whole series after it. Chains of icebergs are sometimes formed in this way in the Arctic seas.” From these observations we deduce the following result:--Snow consists of small particles of ice. Now, if by pressure we squeeze out the air entangled in thawing snow, and bring the little ice-granules into close contact, they may be expected, as they do, to freeze together; and should the expulsion of the air be complete, the squeezed snow will assume the appearance of compact ice.