From William Hopkins   Dec. 27/61

Cambridge | Dec. 27/61

Dear Tyndall,

It will be my object in the glacier paper I am writing¹ to fit and frame the theories of glacial motion together, as far as they harmonize into a consistent whole. I define solidity carefully and call ice solid (not confounding solidity and rigidity as Forbes has always tried to do unjustifiably); and I define viscosity and say that ice cannot be viscous, maintaining that your experiments of the crushing and regelation of ice make it no longer justifiable to call ice viscous. I then introduce my own investigations of the internal tensions and pressures, but worked out by a more general mathematical analysis than heretofore. I don’t attempt to popularize, but to scientific-ize, the subject. I have applied my results to explain the formation of fissures in various cases; also to explain the pressure theory of the veined structure. I have also endeavoured to explain the different ways in which the internal actions may overcome the cohesion, and to point out the mechanical experiments still wanting to render this part of the subject more complete. I also show what I believe to be the impossibility of Forbes’s theory of the veined structure being true. I give a brief account of the sliding of glaciers, in doing which I must necessarily expose Forbes’s ignorance of the nature of the forces called into play by that motion. I am also anxious to make it understood how much effectiveness is given by this sliding movement to the internal pressures and tensions in dislocating the mass. Forbes has attempted to do this by appealing to hydrostatic pressure of the water contained in the pores of the ice. I must necessarily betray his ignorance of this problem, and also his entire misconception of the vis-viva.²

The paper contains more things that have been done before those things that are new, but they have never been put together systematically before. My purpose is to give the subject the most scientific and demonstrative form it will at present admit of. I don’t wish to be controversial, nor do I intend as you will see from this sketch to be historical. I wish to reserve the popular and the historical views for my review in the Quarterly,³ and I should be most thankful to you for any jottings down you may send to me. I shall have my memoir by me 10 days or a fortnight longer, and should be very glad of any further distinct facts about the veined structure. How far is the longitudinal structure continued down the centre of the Aar glacier? The question of transmission is a difficult one. Do the dirt sands on the Mer de Glace coincide with the structure both in the lower and higher parts of the glacier? It appears to me that accurate observations and measurements are still wanting on this subject. Have you heard any thing more about Forbes’s lectures at St. Andrews?

Yours truly, | W. Hopkins.

RI MS JT/1/TYP/2/644–645

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