The Theory of Glacier motion. 89 



glaciers and the apparently rigid nature of ice by postulating 

 that heat is actually developed in glaciers by the intense 

 local pressure in their interior. This heat, he urges, must 

 create temporary fluidity at points and surfaces where the 

 compressing force is a maximum, thereby allowing the 

 particles to slide into new positions, until when, released 

 from the excess of pressure, the mass instantly resumes its 

 rigidity. He argues also that pressure without heat may 

 tend to reduce ice to fluidity. From the fact of water being 

 denser than ice it follows that, if water were cooled down 

 below the freezing point while subjected to pressure, it 

 might be found to remain permanently fluid, whence it 

 would be fair to presume that pressure sufficiently great 

 would restore ice to the more compact form of fluid water. 

 He concludes by suggesting this fact as a possible vera 

 causa of the motion of glaciers (Phil. Mag., XXVI. 495 — 7). 

 This paper, which is very interesting and suggestive, has 

 been largely overlooked. It in fact propounds as an 

 hypothesis a view put forward by Professor James Thomson 

 many years later with considerable force. 



That investigator argued in a paper published in 1849, 

 that the lowering of the freezing point of water ought 

 to amount to '0075° centigrade for every additional atmo- 

 sphere of pressure. His conclusion was experimentally 

 proved by Sir Wm. Thomson in 1850. 



On the basis of this as a postulate. Professor Thomson, 

 in 1857, went on to argue that, "if a mass of slightly porous 

 ice containing water diffused in it at 0° centigrade, be 

 subjected to forces tending to change its form, it will have 

 its melting point lowered below 0° centigrade, and will there- 

 fore begin to melt and in liquefying evolve cold ; the liquefied 

 portions being subjected to squeezing of the compressed 

 mass in which they originate, will spread themselves out 

 through the pores of the general mass by dispersion from 

 the regions of greatest to those of least fluid pressure. This 



