Page:The fairy tales of science.djvu/289

 Various theories have been advanced to account for the motion of glaciers. Saussure, who was the first to observe these wonderful ice-rivers with any attention, asserted that they advance by sliding along their beds, which are constantly lubricated by the melting of the lower strata of ice. But this explanation is far from being satisfactory. Ice is undoubtedly a very slippery substance, but it is scarcely credible that a solid mass of ice some twenty miles in length should glide along by reason of its slipperiness.

To move the Leviathan, our engineers had to make use of the most powerful machines ever constructed before they could overcome the friction between the mighty ship and the surface upon which it rested. But the mass of the Leviathan is immeasurably small compared with that of the glacier; indeed, the river of ice might support a number of such ships, and still move onward at its usual speed. Now, in spite of the lubricating fluid which Saussure imagined to exist between the glacier and its rocky bed, the friction must be immense, and we can scarcely reconcile the steady movement of the frozen mass with the operation of such a powerful retarding force.

Again, it may be asked, how does the huge icicle adapt itself to the irregular form of the valley through which it travels? A solid mass of ice, however large, might possibly slide along a perfectly straight channel, but mere slipperiness would