370 Professors; Tyndall and Huxley on the Structure 



the quantity of ice being rather more than sufficient to fill the 

 gi'oove, and hence projecting above its edge, the pressure brought 

 the fragments together and re-established the continuity of the 

 ice. After a few seconds it was taken from the mould, bent as 

 if it had been a plastic mass. Three other moulds similar to 

 the last, but of augmenting curvature, were afterwards made use 

 of, the same prism being passed through all of them in suc- 

 cession. At the conclusion of the experiments the prism came 

 out, bent to a transparent semi-ring of solid ice. 



In this way, by the proper application of force, all the bend- 

 ings and contortions observed in glacier ice, and adduced in 

 proof of its viscosity, can be accurately imitated. Any observer, 

 seeing a straight bar of ice converted into a continuous semi- 

 ring without being aware of the quality refei'red to, and having 

 his attention fixed on the changes of external form alone, would 

 be naturally led to the conclusion that the substance is viscous. 

 But it is plainly not viscosity, properly so called, which enables 

 it to change its shape in this way, but a property which has 

 hitherto been entirely overlooked by writers upon glaciers. 



It has been established by obsei'vation, that a vertical layer of 

 ice originally plane, and perpendicular to the axis of a glacier, 

 becomes bent, because the motion of its ends is retarded in com- 

 parison with that of its centre. This is the fact upon which the 

 viscous theory principally rests. 



In the experiments with the straight prism of ice, four suc- 

 cessive moulds, gradually augmenting in curvature, were made 

 use of. In passing suddenly from the shape of one to that 

 of the other, the ice was fractured, but the pressui'e bi'ought the 

 separated surfaces again into contact and caused them to freeze 

 together, thus restoring the continuity of the mass. The frac- 

 ture was in every case both audible and tangible; it could be 

 heard and it could be felt. A series of cracks occurred in suc- 

 cession as the different parts of the ice-prism gave way, and 

 towards the conclusion of the experiment, the crackling in some 

 instances melted into an almost musical tone. But if instead 

 of causing the change to take place by such wide steps as those 

 indicated ; if instead of fovir moulds, forty, or four hundred were 

 made use of; or better still, suppose a single mould to have the 

 power of gradually changing its curvature from a straight line to 

 a semicircle under the hydraulic press ; the change in the cur- 

 vature of the ice would closely approximate to that of a truly 

 plastic or viscous body. This represents the state of things in a 

 glacier. A transverse plate of ice, situated between the mass in 

 front of it and the mass behind, is virtually squeezed in a press 

 of the description which has been just imagined. The curva- 

 ture of the ice-mould does change in the manner indicated, and 



