496 Mr. Sutcliffe's Sttggestions on the Movemetit of Glaciers, 



place and the severed portion slides forward under the press- 

 ure which produced the fracture, is probably enormous. 



Now the possibility of thawing ice by friction against itself 

 is considered as established by the experiment of Davy : so 

 that we have a vera causa actually present, the only question 

 being as to the extent and mode of its operation. When fissures 

 actually take place, and one portion of ice slides forward, the 

 film of water produced by the mutual friction of the sides 

 would, on the cessation of motion or its diminution beyond a 

 certain rate, immediately freeze, thereby either obliterating 

 the crack or filling it with a thin plate of half-crystallized ice 

 running as a band through the substance of the glacier. 



That such cases actually occur is highly probable, but my 

 principal object is to suggest the probable effect of suddenly 

 increased pressure, mthout friction, in producing heat and 

 temporary fluidity at points and surfaces where the compress- 

 ing force is a maximum, and thereby allowing the particles 

 to slide into new positions, where, released from the excess of 

 pressure, the mass would instantly resume its rigidity. This 

 momentary development and instant reabsorptionof heat would 

 be strictly analogous to that which raises the velocity of sound 

 in air by* nearly one-fifth beyond the result deduced from the 

 general theory of elasticity. 



II. It deserves consideration how far pressure, apart from 

 its temporary effect in developing heat, may tend to reduce 

 ice to a state approaching fluidity. We know its influence in 

 preventing the conversion of water into steam, and reducing 

 steam to fluid water. It appears in this case to act simply by 

 opposing obstacles to the separation of particles, and by forci- 

 bly bringing them nearer when separated. Now water is 

 denser than ice, and may remain fluid independently of press- 

 ure at temperatures below the freezing- i>oint; though in this 

 case the equilibrium subsisting among the particles is umtahle, 

 and expansion with congelation takes place on the slightest 

 disturbance. 



But if water were cooled below the freezing-point while 

 subjected to pressure, it might probably be found to remain 

 permanently fluid; and in tliis case it would be fair to pre- 

 sume that a pressure sufficiently great would restore ice to 

 the more compact form of fluid water. 



It is particularly to be noticed, that the pressure requisite 

 for condensing steam is very small compared with that which 

 would be required for comi)ressing an incondensible gas to 

 the density of water ; and it may be fairly supposed that the 

 same rule would hold in the liquefaction of ice by pressure. 



The suggestion last offered may be confirmed or disproved 



