140 VISCOUS THEORY OF GLACIER MOTION. [1846. 



8. SUMMARY OF THE EVIDENCE ADDUCED IN FAVOUR OF THE 

 PLASTIC OR Viscous THEORY OF GLACIER MOTION. 



It is often difficult to obtain a calm and full hearing for 

 any new theory or experimental investigation ; not because 

 there is any antipathy to novelty, or that experiment is under- 

 valued, but simply because, in an age of bustle and struggle for 

 pre-eminence, each man is so busy with his own reputation, or 

 the means of increasing it, that he has no leisure to attend to 

 the claims of others ; to which may, perhaps, be added, that in 

 the general diffusion of knowledge and acquirement, each reader, 

 finding something in every course of experiment or reasoning 

 which he knew, or thinks he knew before, is apt to run off with 

 the chain of ideas which that one familiar link suggests, and 

 losing patience to follow an argument of which he thinks he 

 can, by his own penetration, anticipate the close, he sits in 

 judgment on errors which are of his own invention, and confronts 

 the author with arguments and opinions already thrice refuted 

 and rejected by himself. In an age when all men would be 

 teachers, and all write for the press, the lot of an attentive 

 reader falls to few. 



I am far from saying that I have been more than usually 

 unfortunate in this respect. But having, like others, seen my 

 opinions disfigured for want of sufficient attention to apprehend 

 them, or the arguments by which they are supported ; ignor- 

 ance of first principles hinted at, and even errors of observation 

 imputed, where it was convenient that such ignorance and such 

 errors should be presumed ; I claim the privilege of stating 

 afresh, though very briefly, the leading opinions which I do 

 hold, and some arguments for them, which, if not altogether 

 new, may be placed in a new light. 



superposition of the velocities due to local and to general causes, which tends to 

 displace the seasons of maximum and minimum motion, and thus to render the con- 

 nection of velocity with temperature less direct and immediate than it would other, 

 wise be. The middle region of a glacier having a moderate and tolerably uniform 

 declivity is therefore most proper for studying the effects of temperature. Nov. 

 1858.J 



