From William Hopkins   Nov. 3 /60¹

Llwyn Madoc | Builth, S. Wales | Nov. 3 /60.

Dear Tyndall,

I have finished the review of your book² with the exception of a single passage in which I wish to announce the fact of my having read Rendu’s memoir,³ which I have never been able to lay my hands upon.⁴ In writing to Parker⁵ the other day, it occurred to me that the volume of Transactions containing it⁶ might be obtained perhaps from the Royal Society or the Geol. Sec., should you not get back your single copy in time. I want much to see it though; I doubt not, my impression will be the same as that from your section respecting it.⁷ I am glad you do not think of replying directly to Forbes’s pamphlet,⁸ more especially as I have spoken of it myself; and I think your immediate justification (if you can be said to require any at all, which you do not) will come better from me than from yourself. I have insisted on Rendu’s claim to a share of such honour as the first conception of the molecular mobility of glacial ice ought to confer, allowing Forbes all the merit of his persistent endeavours to establish the viscous theory,⁹ but not of being its first originator. I have pointed out also that we have really little concern with the question as a personal one—whether Forbes did justice to Rendu or not in his ‘Travels’. The real question is a much broader one; whether, when the scientific public of this country assigned the whole merit of the Viscous Theory to Forbes, had or had not (thro’ Forbes or anybody else) sufficient means before them of weighing Rendu's merits with his? We had really nothing of the kind. Forbes’s insulated quotations gave no real idea even of what your section gives one. But I want much to bear testimony myself to the character of the real memoir.

Forbes is a selfish, uncandid and ungenerous minded man. If I ever did swear (which I never do) I should say that his d---d Scotch prudence keeps him just on the safe line of propriety beyond which he never tumbles over on the generous side. Such was singularly the case in his dispute with that kindly open-hearted fellow Agassiz, and such has been exactly his conduct towards Rendu. His extracts from Rendu’s memoir are such as might perhaps gain him a verdict against a charge of injustice in a court of scientific law, but in a court of scientific equity and generosity he would be utterly lost. While he makes bald and insulated quotations from Rendu’s memoir he usually tries to bespatter him with more or less of contempt, and has encouraged in a remarkable degree a most unjustly deprecatory tone towards him on the part of his friends and reviewers. He has endeavoured to smother my own views and arguments by ignoring them. He will not find that ruse successful. In some form or other I intend to publish a complete statement of my own views¹⁰ as founded on my own earlier investigations and your recent researches, in which I shall criticize without reserve Forbes’s theoretical reasonings which I regard as contemptible from beginning to end. His attempt to merge your experiments in his theory, in that Jesuitical paragraph¹¹ in his introduction to his Occas. Papers offends me excessively. If his tearing and bruising should be your only process of continued cracking breaking and regelation! If indeed it should be so! The whole passage is a kind of fac simile of the man.

I hope my review¹² won't make you conceited. It is complimentary. I shall be here till the 12th at least.¹³ Don’t forget the memoir. The review is long one for one in Fraser. It will occupy a dozen pages.¹⁴

Yours truly | W. Hopkins.

My knee mends but rather slowly I think I am just mounting my crutches and become a sort of quadruped an instance of a mutation of species perhaps. I shall be glad to resume biped character again, but that will require time. I know not when I shall be scientifically in town again.

Nov. 4.

I could not get my letter off on Saturday¹⁵ and to-day we had no post. I add a few lines more. As you are about to write an article for Fraser,¹⁶ if it be on glaciers and you are likely to write it soon, had you not better see my review before it is printed; unless it appear in the Dec. number, in which case you would gain little by seeing it before hand. As it was impossible for want of space to enter fully into the analysis of glacier theories, this part of the review is but imperfect. I have made some observations on the sliding theory. There is not a fact connected with glacial motion more certain than that glaciers do slide, and that one part of the motion of their surfaces is due to that cause. Your observation makes it about 1/2 of the whole motion; Forbes makes it 5/8. But the curious thing is that, while nobody doubts this, everybody forgets it, apparently because it is independent of the internal structure of the mass. It must however, be recognized in any general view of the motion of a glacier. Till my experiment exemplifying the slow and uniform motion of a block of ice down a plane of small inclination, Forbes used to maintain that if the glacier slided at all, it would descend with an accelerated motion and be discharged into the valley beneath. When he dared no longer to use that argument, he has tried as much as possible to ignore the subject. In one of my letters to the Phil. Mag.¹⁷ I said that both the sliding and viscous theories were founded on verae causae, but that the relative amounts of motion produced by them could only be determined by observation, and I insisted on the determination of the velocities at the surface and bottom of a [1-2 words missing] glacier as the only one which could decide the relative claims of the two theories. I anticipated that a portion of the whole motion would be due to each cause, but my impression was so far erroneous that I expected more would be due to the molecular mobility of the mass. Forbes’s observation at the end of the Glacier des Bois was in fact made at my instigation. Having found the two motions in the ratio of 5/3 in favour of sliding, he has the impudence (I can call it nothing else) to say that the result leaves us no alternative but the adoption of the viscous theory, and, as he evidently means, to the exclusion of the sliding theory which he certainly does thoroughly exclude, for I don’t think he ever mentions it again with reference to my experiment, and only in his notice of De Saussure’s theory¹⁸—the most absurd and illiberal piece of criticism that ever man was guilty of. However the learned professor must be taught that his decision is not final in such matters. Your theory of regelation requires a large crushing force. This I am satisfied is derived principally at any point of the valley where the motion is obstructed from the sliding of the mass in the higher and more unobstructed parts of the valley. An enormous crushing force on an obstructed part of the glacier will thus be produced a tergo,¹⁹ and there comes in so beautifully your regelation, after the change of form permitted by the molecular mobility of the crushed mass and required by the conditions of the glacial valley, has been effected. Where the valley is unobstructed the quicker motion of the centre of the glacier is constantly both by tension and pressure, producing both this infinitesimal cracking (as well as finite fissures) and consequent molecular mobility. I very much doubt whether a glacier would move at all if it were every where totally incapable of sliding. Forbes has felt the want of a force of this kind to bring his viscosity into play and his endeavour to find it in his “enormous hydrostatic pressure” the most blundering bosh that ever was written. I alluded to the passage you have quoted from the third Part of the Royal Society Memoir.²⁰ Well may you say you don’t perfectly understand it. But all this requires careful and accurate development. I have not yet said any thing about it in the review. I may add a paragraph about it.²¹ I wish I could see the review of your book in the New Edin. Ph. Jour.²² I don’t wish of course to make my review an answer to any ignorant fellow who may choose to abuse you in that periodical, but if there be any thing to which I could indirectly reply I would do so, if you think it worth while to get me a copy thro’ Parker.

Your smashing of Forbes’s absurd ripple theory²³ is complete. What will become of his differential theory of the veined structure without his ripples?

Your elucidation of the internal pressures and tensions of a glacier, due to the more rapid motion of the centre, will be very valuable. Forbes’s friends in the plentitude of their ignorance, may ignore a mathematical investigation which neither they nor their readers can understand, but they cannot so easily ignore the conversion of your circle into an oval, and the obvious inferences therefrom. It only recently occurred to me how simply your diagram would determine also the line of greatest differential motion. It is manifestly that in which the difference between two consecutive radii drawn from the centre to the circumference of the oval, is greatest along C A and C B the directions of greatest tension and pressure it is zero, and a max. along C P which (the oval being but little elongated) will manifestly be inclined at 45° to each of the above lines. Would it not be well to add this in your next edition?²⁴ It comes so directly to the point. That Forbes should have mistaken C A for C B is nothing to be surprised at; it is in accordance with all his other mechanical blunders and obscurities; but that Whewell²⁵ should have copied him only shows the blundering hurry in which he does all such things.

Nov. 5th

I got my letters unexpectedly yesterday. I find my review must be in the hands of the editor of Fraser by the 15th.

Don’t be afraid of Forbes and his sychophants. I'll support you. With the sense of having truth on our side we can fight with better temper than they can, and it will be strange if men of science, experimental and mathematical, can’t beat “Authorities of the press.”

I am mending though slowly. I have no pain but the knee remains stiff and swelled and the leg of course useless to me at present.²⁶

Yours truly | W. Hopkins.

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