168 VISCOUS THEORY OF GLACIER MOTION. [184G. 



itself, and even the closely adjoining expansion of the interior 

 surface, carefully and perfectly clean. Yet when the protrusion 

 of the ice cylinder took place, the surface of it, even at the 

 height of an inch or two ahove the neck of the bottle, was 

 smeared with red colour. In one of the specimens the definite 

 ring of red was, as it were, transferred from its position on the 

 internal expansion of the bottle to the surface of the compara- 

 tively narrow cylinder of ice which had been discharged through 

 the aperture. Now this could not possibly have occurred unless 

 the plastic substance of the ice had been forced laterally and by 

 a converging pressure from all sides (up 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 Frontispiece, Plate VI.*fig. 1, 

 taken from a coloured chalk sketch made at the time* from one 

 of these experiments, will explain more distinctly my meaning. 

 It shows the impress of the coloured ring transferred from the 

 comparatively large surface whence it was derived to the cylinder 

 of small diameter into which it has been compressed. Figure 

 2 shows the appearance of the protruded ice when partly thawed, 

 the curved surfaces of air-bubbles indicating the graduated effect 

 of friction as the distance varied from the glass, which appears 

 to be consistent only with a molecular plasticity of the ice. In 

 these experiments the slow progress of congelation of the interior 

 water, which is the source of the intense pressure, is eminently 

 favourable to their development, while it also bears some analogy 

 to the extremely gradual internal movements of a glacier. 

 Were it attempted to produce by intense pressure acting for a 

 few minutes what we here produce in many hours, or even some 

 days,t the effect, though perhaps externally analogous, would be 

 deficient in the evidence of plasticity. Nov. 1858.] 



* [In the winter 1846-7, if I recollect rightly.] 



f [Mr. Christie's experiment lasted several days. His letter, which is now 

 before me, is dated 4th April 1846.J 



