Mr, Hopkins's Remarks on Prof. Forbes's Reply. 59*1 



uniting little modesty with little knowledge set up their own 

 vague conclusions against the demonstrative results of the 

 mathematician, we pass them in silence; but when the appli- 

 cability of such results is denied by men of totally different 

 character, men of high scientific position and acquirement, 

 we expect from them not vague and general assertion, but 

 explicit reasons for their objections. This is what Professor 

 Forbes has not even attempted to do with reference to my 

 investigations on the subject before us. Still had he insisted 

 on the inadmissibility of all theoretical investigations, he might 

 have been at least consistent; but while he denies the admis-? 

 sibility of my solutions, he would call upon us to repose our 

 faith in his own, involving as they do the same properties of 

 matter, and leading to conclusions demonstrably erroneous. I 

 assert that Prof. Forbes has given no mechanical sohition of 

 the problem before us as regards the internal pressures and ten- 

 sions called into action by the peculiar motion of a glacier, and 

 therefore no physical explanation of the laminar structure. He 

 may assert, that in allowing the probability of that structure 

 being due in some x^ay to the motion, I am really admitting 

 the correctness of his theory; I can only reply, that if our views 

 are mechanically the same, I should be at a loss to say what 

 constitutes a real difl'erence of mechanical views on the sub'?- 

 ject. 



Hitherto I have spoken with reference to the mechanism 

 of glacial motion independently of its cause. In my first 

 memoir my object was to explain how the motion of a glacier 

 might take place according to the sliding theory, hypotheti- 

 cally regarding glacial ice as having only a small degree of 

 plasticity, and a glacier to be a dislocated mass. In my se- 

 cond memoir I endeavoured to point out certain characters 

 which would distinguish the motion, under other hypotheses 

 respecting the constitution of the glacial mass. I made four 

 different hypotheses, and my conclusion was, tliat none of 

 them could be correct, and yet this memoir- has been cited as 

 a proof that 1 had altogether modified my views on the sub- 

 ject and almost adopteil those of Professor Forbes, though 

 the Professor at the same time complains of my having, in 

 the same memoir, so summarily dismissed his whole theory. 

 I could not however both adopt his views and summarily 

 reject them, and I might as well have been charged with the 

 simultaneous adoption of all the four hypotheses 1 had made, 

 as with that of any one of them in particular. They were 

 made with the view of testing their admissibility, but rejected 

 as leading to conclusions inconsistent as I believed with ob- 

 servation. Thus I considered the hypothesis gf the whole or 



