L20 Mr. H. H. Howorth on 



sides, and (2) for the most part, most rapid near the lower 

 extremity of glacier, but varying rather with the transverse 

 section than the length. (3) That it is more rapid in summer 

 than in winter, in hot than in cold weather, and especially 

 more rapid after rain, and less rapid in sudden frosts. (4) It 

 is farther in conformity with what we know of the plas- 

 ticity of semi-fluids generally, especially near their point of 



fusion such as sealing-wax, for example, exposed for 



a long time to a temperature far below their melting heat,, 

 and which have moulded themselves to the form of the sur- 

 faces on which they rest. (5) When the ice is very highly 

 fissured, it yields sensibly to the pressure of the hand,, 

 having a slight determinate play, like some kinds of lime- 

 stone, well known for this quality of flexibility. (6) Such 

 a condition of semi-rigidity accounts for the remarkable 

 veined structure which pervades it. 



Meanwhile the observations of Forbes, and especially his 

 claims to have discovered the veined structure of ice, were 

 contested by Professor Agassiz, in a memoir published in 

 the same magazine (Vol. XXXIII., 265, etc.); and thus began 

 a scientific feud which was not only deplorable in itself, but 

 eventually led to a very serious injury to science itself I 

 would here remark, that in this paper Agassiz reiterates his 

 adhesion to the dilatation theory, and to the conclusion that 

 glaciers do not move in winter, but only in summer. 



Forbes continued to press his views as to the viscosity 

 of glacier ice, and notably in his well known "Travels," 

 published in 1843. In this work he writes, "^ glacier is 

 an imperfect fluids or a viscous body^ which is icrged down 

 slopes on a certain inclination by the mutual pressure of its 

 parts'' He compares glacier ice to a moderately thick mortar 

 or the contents of a tar barrel poured into a sloping channeU 

 " Either of these substances," he says, " without actually 

 assuming a level surface will tend to do so. They will 

 descend with different degrees of velocity, depending on 



