From one thing only did M. Rendu shrink; and it is _the_ thing regarding which we are still disunited. He shrank from stating the physical quality of the ice in virtue of which a glacier moved like a river. He demands experiments upon snow and ice to elucidate this subject. The very observations which Professor Forbes regards as proofs are those of which we require the physical explanation. It is not the viscous flow, if you please to call it such, of the glacier as a whole that here concerns us; but it is the quality of the _ice_ in virtue of which this kind of motion is accomplished. Professor Forbes sees this difference clearly enough: he speaks of "fissured ice" being "flexible" in hand specimens; he compares the glacier to a mixture of ice and sand; and finally, in a more matured paper, falls back for an explanation upon the observations of Agassiz regarding the capillaries of the glacier.[L]
[A] Expressions such as "last summer," "last autumn," "recently," will be taken throughout in the sense which they had in the early half of 1860, when this book was first published.--L. C. T.
[I] At page 38 of the 'Travels' the following passage also occurs:--"I believe that I may safely affirm that not one observation of the rate of motion of a glacier, either on the average or at any particular season of the year, existed when I commenced my experiments in 1842."
[L] In all that has been written upon glaciers in this country the above passages from the writings of Rendu are unquoted; and many who mingled very warmly in the discussions of the subject were, until quite recently, ignorant of their existence. I was long in this condition myself, for I never supposed that passages which bear so directly upon a point so much discussed, and of such cardinal import, could have been overlooked; or that the task of calling attention to them should devolve upon myself nearly twenty years after their publication. Now that they are discovered, I conceive no difference of opinion can exist as to the propriety of placing them in their true position.
The measurements of Agassiz and Forbes completely verify the anticipations of Rendu; but no writer with whom I am acquainted has added anything essential to the Bishop's statements as to the identity of glacier and liquid motion. He laid down the conditions of the problem with perfect clearness, and, as regards the distribution of merit, the point to be decided is the relative importance of his idea, and of the measurements which were subsequently made.