EEGELATION THEORY OF TYNDALL. 



63 



The velocity of motion is small in the same proportion as the viscous 

 mass is stiff. The descent of the Mer de Glace from the cascade of the 

 Glacier du Geant to the point of Glacier de Bois, a distance of ten miles, 

 is 4,000 feet. Water, under these circumstances, would rush with fear- 

 ful velocity. The glacier moves but two feet in twenty-four hours. 



Such viscosity of ice as supposed by Forbes is now proved by ex- 

 periments. Ice-boards supported at the two ends bend into an arc 

 under their own weight. Cylinders of snow compacted into ice may 

 be bent in the hand to a semicircle without rupture,* and bars of ice 

 may even be stretched by slow pulling, f 



Regelation Theory of Tyndall. 



If ice be indeed a viscous body, then there seems no reason why it 

 should not yield to pressure even in small masses, if the pressure be 

 sufficiently slowly graduated. In the hands of a skillful experiment- 

 alist it ought to exhibit this property. Prof. Tyndall tried the ex- 

 periment. Masses of ice of various forms were subjected to slowly- 

 graduated, hydrostatic pressure. In every case, however slowly grad- 

 uated the pressure, the ice broke ; but if the broken fragments were 

 pressed together, they reunited into new forms. In this manner, ice in 

 the hands of Prof. Tyndall proved as plastic as clay : spheres of ice 

 (a, Fig. 54) were flattened into lenses (#), hemispheres (c) were changed 



T<I>F 



njf 



Fig. 54.— A B C, molds; a c > 



original forms of the ice; b df, the forms into which they 

 were molded. 



into bowls (d), and bars (e) into semi-rings (/). He even asserts that 

 ice may be molded into any desirable form ; e. g., into vases, statuettes, 

 rings, coils, knots, etc. Here, then, we have a power of being molded 

 such as was not dreamed of before ; but this power was not depend- 

 ent on a property of viscosity, but upon another property long known, 

 but only recently investigated by Faraday, viz., the property of rege- 

 lation. 



* Aitkin, American Journal of Science, vol. v, p. 305, third series, 1873. 

 f American Journal of Science, vol. xxxiv, p. 149, 1887 ; and Nature, vol. xxxix, p. 

 203, 1888. 



