The Theory of Glacier motion. 135 



acts otherwise than conformably to the law of semi-fluid 

 motion ; all he denies is that ice is of a gluey tenacity, and 

 will stretch like a plastic substance. 



We will now turn to Tyndall's own theory. This 

 theory, which he applied to the motion of glaciers, 

 was based upon a fact first published by Faraday in a 

 lecture at the Royal Institution as early as 1855, according 

 to which "when two pieces of ice with moistened surfaces are 

 brought into contact they become cemented together by the 

 freezing of the film of water between them, while, when the 

 ice is below 32^ Fahr., and therefore dry, no effect of the 

 kind can be produced " (See Glaciers of the Alps, 357). 



" A generalization from this interesting fact," says 

 Tyndall, " led me to conclude that a bruised mass of ice, if 

 closely confined, must recement itself when its particles are 

 brought into contact by pressure" (id.). He therefore appeals 

 to certain experiments which had, in fact, been made in a 

 •different way by others. 



In a letter addressed to Forbes, on April 4th, 1846, by 

 Mr. Christie, Secretary of the Royal Society, that gentleman 

 instanced the experiment of filling a hollow iron shell with 

 water, and exposing it to frost with the fuze hole upper- 

 most, when the water will freeze, and protrude a cylinder of 

 ice from the fuze hole, and as the experiment is continued 

 the fuze continues to grow, in proportion as the water 

 freezes. " No thawing takes place in the process. Does not 

 this show plasticity even in very small masses of ice ? " says 

 Mr. Christie. The experiment was repeated by Forbes in 

 glass vessels which could be closely watched. He first put 

 a ring of a greasy matter of a red colour round the inside of 

 the vessel, keeping the aperture clean. When the ice pro- 

 truded it was found incased with red, in some cases in the 

 form of a red ring, which, as he says, could not have been 

 unless the plastic substance of the ice had been forced 

 laterally, and, by a converging pressure from all sides, up 



