A GLACIER IS NOT A MASS OF FRAGMENTS. 
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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 ; ignorance of 
first principles hinted at, and even errors of observation imputed, where it was con 
venient that such ignorance and such errors should be presumed ; I claim the privi- 
lege 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. 
My chief analogies for the illustration of glacier motion have been drawn from 
the motion of a river, and by that comparison it in a great measure stands or falls. 
Slight and partial as is our knowledge of the mechanics of imperfect fluids, the ex- 
planation which I have given is founded upon that knowledge, and it appears to me 
to be sufficiently precise to warrant the inference of an identity of the mechanism in 
the two cases ; — namely, that the movement is due to the internal pressures, arising 
from the weight of the mass, communicated partly or principally in the manner of 
hydrostatic pressure throughout a body whose parts are capable of moving or being 
shoved over one another (by that exertion of force which Dr. Thomas Young calls 
Detrusive Force*, which overcomes what is commonly called the Friction of Fluids), 
so that the velocities vary from point to point of the moving body, being most rapid 
near the surface and centre, and least so near the banks and bottom. 
So viscous fluids move, so bodies (even brittle solids, such as hard-boiled pitch) 
possessing the ordinary properties of solid bodies often do, if sufficient time and 
sufficient force be allowed-^ ; the efficiency of time being chiefly this, that a pressure 
insufficient to produce instant detrusion, will, sooner or later, cause the particles to 
slide insensibly past one another, and to form new attachments, so that the change of 
figure may be produced without positive rupture, which would reduce the solid to a 
heap of fragments. This change may either take place without any loss of homoge- 
neity, or by numerous partial and minute rents not everywhere communicating, and 
therefore not necessarily destructive of cohesion, which may be termed a bruise. 
A glacier is not a mass of fragments . — As the analogy of the glacier to a river, in 
which the fluid principle is greatly in defect, and the cohering or viscous principle 
is greatly in excess, is the theory which I maintain, it is evident that the analogy of 
a stream of sand, or loose materials shot from a cart, or any other comparison with 
an aggregate of incoherent fragments or individual masses, must be wrong if mine 
be right. And I feel confident, not only that such an incoherent mass could not 
move after the manner of a glacier, but also that attentive inspection of a glacier at 
once contradicts such an idea. 
* Lectures, I., 135. 
f See Professor Gordon’s Experiment, Philosophical Magazine, March 1845. 
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