WHAT IS A GLACIER? 3 



in it, and plugged the aperture up. lie then subjected the 

 cylinder to intense cold till the whole was two or three de- 

 grees below the freezing-point of water. But that the water 

 remained liquid was evidenr from the fact that, upon shaking 

 the cylinder, the bullet inside rattled about as at higher tem- 

 peratures : while, upon removing the plug so as to relieve 

 the pressure, the whole was instantly converted into solid 

 ice. Various similar experiments have been made in which. 

 upon removal of the plug, the water ejected from the aperture 

 by the expansive power of the cooling water within the 

 cylinder immediately freezes, and forms a projecting column 

 of ice several inches in length. It was at first thought that 

 this projecting column illustrated the plasticity of ice ; but 

 it is now pretty certain that it illustrates, rather, the curious 

 effect of pressure upon the freezing-point of water. 



The capacity of water at the freezing-point to transform 

 itself, under varying degrees of pressure, from the solid to 

 the liquid state, and vice versa, is illustrated by another ex- 

 periment, ascribed by Professor Tyndall to Mr. Bottomley. 

 A copper wire was looped over a bar of ice about four inches 

 square, and a weight of twelve or thirteen pounds was sus- 

 pended from it. The pressure under the wire caused the ice 

 in immediate contact with it to melt ; but. as the resulting 

 water escaped arouud the wire, and was relieved from press- 

 ure, it immediately froze, and cemented together again the 

 walls of ice above the wire. In half an hour the wire had 

 cut completely through the bar of ice. and yet the whole 

 breach above it was repaired, and the bar was intact. 



This capacity of fragments of ice. when near the melting- 

 point, to freeze together when their faces are joined, can be 

 readily observed in a variety of experiments. When two 

 pieces of ice in a basin of warm water are brought together 

 they will immediately adhere. If a cake of ice whose tem- 

 perature is near the melting-point be placed in a mold and 

 subjected to pressure, the first result is to break it into pieces ; 

 but, on continuing the pressure, the particles reunite and 

 freeze together into a shape corresponding to that of the 



