The Theory of Glacier motion. 139 



traversed here and there by fissures and cracks, these no 

 more justify us in speaking of glacier ice as porous than the 

 joints and fissures in a slate quarry give us a right to term 

 slate porous. We do not call iron porous because water 

 runs out of a cracked kettle" (^Phil. Mag. 4th ser. xiv. 250). 



This conclusion of Professor Huxley seems absolutely 

 fatal to Professor Tyndall. As Dr. J. Ball says, " If we are 

 to adopt his conclusion, then we must cease to believe with 

 Professor Tyndall, that glacier ice is enabled to advance in 

 conformity with the law of viscous motion, by fracture and 

 regelation " {Phil Mag., 4th sen, xiv. 502). 



When we turn from these to another series of facts, 

 whose lesson is ignored by Professor Tyndall, namely, the 

 proved differential motion by which every point from the 

 centre of a glacier to the side, from its summit to its base 

 has a different motion, we have a condition which seems 

 to me compatible only with semi-fluid motion, and utterly 

 unexplainable by any theory of crushing and regelation. 



Referring to Moseley's argument on the sheanng force 

 of ice, Mr. Trotter says : — " It seems to be decisive against 

 the belief that the ordinary comparatively undisturbed 

 motion of a glacier along a moderately sloping bed takes 

 place by fracture and regelation. Moseley's value of the 

 shearing strength of ice, which has been shown to be 

 enormously too great as a measure of the resistance of ice 

 to slow shearing, would appear on the other hand to be an 

 inferior limit to the resistance to'the shearing fracture which 

 must precede regelation" {Proc. Roy. Soc.y xxxviii. 108). 



Again, Professor Tyndall refers to experiments of his 

 own upon the Mer de Glace, showing its motion in winter 

 when the estimated temperature was 5 degrees below zero 

 centigrade. How, at such temperatures, can regelation 

 occur at all ? The ice surfaces would be all dry and incapable 

 of freezing together. We must remember that it is only 

 damp surfaces that will freeze together again. Professor 



