From William Hopkins   Mar. 26. 61

22 Grand Parade | Brighton. | Mar. 25. 61.

My dear Tyndall,

I was exceedingly amused at the idea of your having Sir D. Brewster¹ and Blackie² at your feet petitioning for an article on Glaciers! Has some great physical revolution taken place in the hyperborean regions of Scotland that has melted down the moral hardness of these northern glacialists? Well, it is funny, but all right. What answer have you to the invitation. We shall hear very little more I suspect of these viscous gentlemen.

Your experiments and observations, in proving that a mass of ice changes its form and adapts itself to external conditions by actually cracking and breaking, and not by a continuous sliding of one constituent article cast another as in a viscous substance, is no unimportant step in the mechanical view of the notion. In fact, it removes the solution from dynamics to statics. We can do little with the dynamical problem of the motion of a viscous substance, but we can do much bearing on the question before us with respect to the statical pressures and tensions of a mass previously to its breaking, and therefore in determining also the directions in which it will break. Whether a glacier constituted as it is would have any considerable motion or not, if it adhered absolutely to bottom on which it rests, I know not, but I am sure of this, that the fact of its sliding along its bed must necessarily increase enormously the forces which tend to break and rupture the ice. This has never yet been pointed out, but it shows the important connexion existing between the motion due to sliding and that due to the finite and infinitesimal breaking of the mass. I think now of writing a short memoir for the Royal Society³ on this subject without waiting for the experiments which I suggested to you in my last, but indicating them as essential for the completeness of the subject. If you can’t find time to make them hereafter, I will try to make them myself.

The lecture I half promised you for the Institution⁴ this spring I must decline for the present. My knee⁵ though slowly and steadily improving is still but a feeble knee, and will keep me here for some time longer, though I hope ultimately to be not much the worse for the accident. I have declined one or two other lectures for the same reason. I want in the first place to write this short memoir, and then I should like much to write a general review of the whole subject for the Quarterly,⁶ if Murray⁷ would admit it. I don’t recollect a glacial review in that journal. I don’t know Murray personally. You do I presume. Can you ascertain for me whether such a review as I should propose would be accepted. I should endeavor to make it philosophical and important, and as little personal as possible.

I have not been experimenting on the transmission of heat thro’ gasses. The paper of mine you allude to⁸ was on the construction of a calorimeter for measuring the absolute (not merely the relative) quantity of heat which emanates from a given surface through air. I don’t attempt to make a distinction between the quantity passing by radiation proper, conduction, convection &c. That is a problem of great interest and I am glad to hear that you are cogitating on it.

I hope I shall get bodily into the scientific world again next month, but I must try to be patient.

Yours truly | W. Hopkins

RI MS JT/1/TYP/2/639–40

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