136 Mr. H. H. Howorth on 



even to the particles in contact with the interior of the 

 glass, so as to be forced through the contracted outlet as a 

 tenacious fluid under its own pressure, or a plastic solid 

 subjected to a considerable force would do under like 

 circumstances. The success of these experiments Forbes 

 attributes to the slowness of the process of congelation 

 employed, which lasted several hours, or, in Mr. Christie's 

 case, several days, and which therefore affords analogies 

 with the gradual internal movements of a glacier {The 

 Theory of Glaciers^ \6\ and i68). 



To turn to Tyndall's experiments, he tells us how in the 

 course of them, moulds of various forms were hollowed out 

 in boxwood, and pieces of ice were placed in them and 

 subjected to pressure. In this way spheres of ice were 

 flattened into cakes, and cakes formed into transparent 

 lenses. A straight bar of ice, six inches long, was passed 

 through a series of moulds augmenting in curvature, and 

 was finally bent into a semi-ring. A small block of ice was 

 placed in a hemispherical cavity, and was pressed upon by 

 a hemispherical protuberance, not large enough to fill the 

 cavity ; the ice yielded, and filled the space between both, 

 thus forming itself into a transparent cup. In short, he 

 says, every observation made upon glaciers and adduced by 

 writers on the subject in proof of the viscosity of ice was 

 shown to be capable of perfect imitation with hand speci- 

 mens of the substance {Glaciers of the Alps, 321). So 

 far there was nothing on the surface to traverse 

 Forbes's views in regard to ice being viscous, but 

 the contrary, as Tyndall himself says. "The experi« 

 ments prove to all appearances that the substance is 

 even much more plastic than it was ever imagined to be by 

 the founders of the viscous theory" {id.)\ but in the case of 

 these experiments the inference would not have been quite 

 correct. The process by which the ice was moulded into 

 shape in them did not involve a continuous flow of semi- 



