IN CLOUDS AND RIVERS, ICE AND GLACIERS. 



perience of the substance. 



409. Take a mass of ice ten or even fifteen 

 cubic feet in volume ; drpw a saw across it 

 to a depth of half an inch or an inch ; and 

 strike a pointed pricker, not thicker than a 

 very small round tile, into the groove ; the 

 substance will split from top to bottom with 

 a clean crystalline fracture. How is this 

 brittleness to be; reconciled with the notion 

 of viscosity ? 



410. We have, moreover, been upon the 

 glacier and have witnessed the birth of cre- 

 vasses. We have seen* them beginning as 

 narrow cracks suddenly formed, days being 

 iL'Ljuired to open them a single inch. In 

 many glaciers fissures may be traced narrow 

 and profound for hundreds of yards through 

 the ice. What does this prove? Did the 

 ice possess even a very small modicum of 

 that power of stretching, which is character- 

 istic of a viscous substance, such crevasses 

 coul'i not be formed. 



411. Slill it is undoubted that the glacier 

 moves like a viscous body. The centre ilows 

 past the sides, the top flows over the bottom, 

 and the motion through a curved valley cor- 

 responds to fluid motion. Mr. Mathews, 

 Mr. Froude, and above all Signer Bianconi, 

 h;ive, moreover, recently made experiments 

 on ice which strikingly illustiate the flexibil- 

 ity of the substance. These experiments 

 merit, und will doubtless receive, lull atten- 

 tion at a future time. 



61. REGELATIOX THEORY. 



412. I will now describe to you an attempt 

 that has been made of late years to reconcile 

 the brittleness of ice with its motion in gla- 

 ciers. It is founded on the observation, 

 made by Mr. Faraday in 1850, that when 

 two pieces of thawing ice are placed to- 

 gether they freeze together at the place of 

 contact. 



ii:. This fact may not surprise ^^d ; still 

 it ;U (.idsed Mr. Faraday and others, and 

 in (i or very great distinction in science have 

 differed in their interpretation of the fact. 

 The difficulty is to explain where, or how, in 

 ice already thawing the cold is to be found 

 requisite to freeze tne film of water between 

 the two touching surfaces. 



414. The word Regelaiion was proposed by 

 Dr. Hooker to express the freezing together 

 of t\vo pieces of thawing ice observed by 

 Faraday ; and the memoir in which the term 

 was first used was published by Mr. Huxley 

 an;! ilr. Tyncla'.l in the Philosophical Trans- 

 actions for I8,"i7. 



415. The fact of regulation, and its appli- 

 cation irrespective of the cause of rcgelation, 

 may be tnus illustrated : Saw two slabs 

 from a block of ice, and bring their flat sur- 

 faces into contact, ; the}' immediately freeze 

 together. Two platen of ice, laid one upon 

 the other, with flannel round them over 

 night, ate sometimes so firmly frozen in the 

 morning that they will rather break else- 

 whei'e Uum along their surtV.ee of junction. 

 If you erter one of the dripping ice-eaves of 

 Switzerland, you have only, to press for a 



'moment a slab of ice against the roof of tLe 

 uave to cause it to freeze there and stick to 

 tfhe roof. 



416. Place a number of fragments of ice 

 in a basin of water, and cause them to touch 

 each other ; they freeze together where they 

 touch. You can form a chain of such frag- 

 ments ; and then, by taking hold of one end 

 of the chain, you can draw the whole series 

 after it. Chains of icebergs are sometimes 

 formed in this way in the Arctic seas. 



417. Consider what follows from these ob- 

 servations. Snow consists of small particles 

 of ice. Now if by pressure we squeeze out 

 the air entangled in thawing snow, and bring 

 the little ice-granules into close contact, they 

 may be expected to freeze together ; and if 

 the expulsion of the air be complete, the 

 squeezed snow may be expected to assume 

 the appearance of compact ice. 



418. We arrive at this conclusion by rea- 

 soning ; let us now test it by experiment, 

 employing a suitable hydraulic press, and a 

 mould to hold the snow. In exact accord- 

 ance with our expectation, we convert by 

 pressure the snow into ice. 



419. Place a compact mass of ice in a 

 proper mould, and subject it to pressure. It 

 breaks in pieces ; squeeze the pieces forcibly 

 together ; they reunite by regelation, and a 

 compact piece of ice, totally different in 

 shape from the first one, is taken from the 

 rress. To produce this effect the ice must bo 

 in a thawing condition. When its tempera- 

 ture is much below the melting-point it is 

 crashed by pressure, not into a pellucid 

 mass of another shape, but into a white 

 powder. 



430. By means of suitable moulds you 

 may in this way change the shape of ice to 

 any extent, turning out spheres, and cups ; 

 and rings, and twisted ropes of the sub- 

 stance ; the change of form in these cases 

 being effected through rude fracture and re- 

 gelation. 



421. By applying the pressure carefully, 

 rude fracture may be avoided, and the ice 

 compelled slowly to change its form as if it 

 were a plastic body. 



422. Now our first experiment illustrates 

 the consolidation of the snows of the higher 

 Alpine regions. The deeper layers of tha 

 neve have to bear the weight of all above 

 them, and are thereby converted into more or 

 less perfect ice. And our last experiment 

 illustrates the changes of form observed upon 

 the glacier, where, by the slow and constant 

 application of pressure, the ice gradually 

 moulds itself to the valley which it fills. 



423. In glaciers, however, we have also 

 ample illustrations of rude fracture and re-ge- 

 lation. The opening and closing of crevasses 

 illustrate this. The glacier is broken on the 

 cascades and mended at their bases. When 

 two branch glaciers lay their sides together, 

 the regelatiou is so firm that they begin im- 

 mediately to flow in the trunk glacier as a 

 single stream. The medial moraine gives n 

 indication by its slowness of motion that it ib 

 derived from the sluggish ice of the sides o 



