594- Mr. Hopkins's Remarks on Prof. Forbes's Reply. 



perpendicular to each other. He has given a diagram to il- 

 histrate his views, but I never saw lines intended to establish 

 a geometrical proposition so singularly ambiguous. I allude 

 to the lines in fig. 2 of the Professor's reply, representing the 

 lines of structure. To preserve their consistency with all 

 those of the same famijy which have preceded them elsewhere, 

 they ought to turn gradually towards the axis and finally 

 cross it at right angles ; but they would betray the cause for 

 which they are here called into requisition, unless they curved 

 themselves the contrary way, as in the annexed diagram, so 



as never to cross the axis at all. In what direction the lines 

 in the Professor's diagram are intended to curve I know not, 

 but it is only when they curve as in the above diagram that 

 the crevasses perpendicular to them can be such as represented 

 in this or Prof. Forbes's figure. It is not for me to reconcile this 

 form of the structural curves with that which the Professor has 

 always assigned to them. But it was scarcely worth while 

 perhaps to dwell at all on this point, since the Professor has 

 given up his explanation of the formation of the crevasses, by 

 the admission of the error he had made in concluding that the 

 direction of maximum tension coincided with that of the loops. 

 It was in controverting his opinion on this point that I was led 

 to make the remarks which the Professor has incorrectly re- 

 presented as a misstatement of his theory, except so far as he 

 may himself have misstated it. 



Again, the Professor asserts that I have misrepresented 

 facts, because I have asserted that no experiments have been 

 made to prove that the plasticity of glacial ice is really greater 

 than common inspection might lead us to suppose. I mean 

 by that assertion that no such experiments have been made 

 independent of the phaenomena to be accounted for. Different 

 explanations are given of those phaenomena by two different 

 theories. According to one, they indicate a property of gla- 

 cial ice which is alone sufficient to account for glacial motion ; 

 according to the other, they are only the necessary conse- 

 fluences of a totally independent cause of motion. How then, 

 m discussing the contending claims of the two theories, can 



