Review oj the Controversy Regarding the Motion of the Glacier. 75 



of ice by a sories of experiments, and applying his results to the j^Ter 

 de Glace, concluded that in the conditions under which the ice in that 

 glacier moved, the unit of shear could rot be less than 75 lbs. per 

 square inch, whereas, gravitation could only produce the observed 

 movement of the glacier, en the supposition that the unit of shear did 

 not exceed 1.3489 lbs. per square inch. So vast a difference 

 between the two — the required force being between fifty and sixty 

 times as great as that which could be allowed to gravity — led Mr. 

 Moseley to sura up his results by saying, that "the IMer de Glace would 

 only descend by its weight, if the ice were of the same degree of hard- 

 ness as soft putty, and of the same specific gravity." "The unit of 

 shear," he says, "in soft putty, is from 1^ to 3 lbs. per square inch.' 

 The mechanical objection has never been refuted, and at the present 

 day the theory that ascribes viscosity to glacier ice can only be said 

 to exist on account of the lack of any other to take its place. 



Canon Moseley, it is true, put forward a theory of his own, after 

 having so seriously assailed that of Mr. Forbes. He proved by experi- 

 ment that a plate of lead, lying on an inclined plane, and subject to 

 alternations of heat and cold, gradually creeps down the plane, and 

 with force sufficient to draw out nails if it had been secured by them 

 to the plane. From this he was led to the opinion that a glacier under 

 changes of temperature, must, in like manner, creep down its sloping 

 bed, in consequence of the alternate expansion and contraction that 

 must ensue. But he seems to have overlooked the fact revealed by 

 some of Agassiz' experiments, that the body of a glacier does not 

 share the changes of temperature that prevail on its surface. The 

 possible limits, therefore, between which the temperature of a pk'eier 

 can vary, are too slight to afford sufficient exjiansion even to a substance 

 so expansible as ice.* Moreover, as has been well pointed out by 

 Mr. Grose, of the English Geological Survey, "it follows, that a glacier, 

 instead of moving more rapidly" (as in the case) "during summer than 

 in winter, should, according to Mr. Moseley's theory, have no motion in 

 summer whatever,"t — the range of temperature attributed to the glacier 

 being between limits absolutely incapable of effi^cting the expansion of 

 the ice in the smallest degree. "| 



This fourth theory of glacier motion having been disposed of, the 

 field was left comparatively clear, but for some time no competitor 

 appeared to claim the dangerous honor. Faraday's discovery of 

 regclation seemed to suggest a m.ethod of accounting, in some degree, 

 for the continuity of the mass during its motion. He found that two 



*The co-efficient of the expansion of ice is .00(i(i2i-56' for 1° Fah. It is, therefore, twice ae 

 dilatable as lead, and more so than any other known solid body. 



fi. E. d- D. Fhih. Maj., Sept., 1870. XL. E. & D. Pfiilo. Mag., -Ith Series. Vol. x. p. 303. 



