James David Forbes to Faraday   14 August 1858

Pitlochry | Perthshire | 14 Aug. 1858

M. Faraday Esq | &c &c &c

My dear Sir

I was very much obliged to you for your letter of the 23d July¹ - & especially for the expressions of regard which it contains & which I can assure you that I heartily reciprocate.

I am also much obliged by your remarks on my little paper²; on which I shall not trouble you with more than a few additional words.

I hope however that you will resume consideration of a subject which you are so well able to illustrate & which is still to a certain extent obscure.

I cannot doubt that regelation takes place between Ice & Metals. The pile of shillings, though perhaps the simplest is not the only experiment I have tried; but is so easy that I hope you will repeat it. I have frozen in like manner a Bronze Letter presser of several pounds weight firmly to ice in a warm room: but this requires a long time.

I do not see any thing contradictory to the views which I have advanced, in the other experiments you mention. The finely triturated Ice - or Mr. Harrisons³ crystalline laminae when in contact with an indefinite mass of water clearly belong to the portion of the curve in my figure between N and O, or to the physical boundary between water & Ice having a temp. intermediate between 31.7 and 32.0 & possessing the plastic quality proper to that intermediate state, just as in the case of wax, tallow, or fusible metal, when portions brought into contact by a gentle pressure become moulded into one another’s substance by molecular cohesion. Further in the case you mention where a quantity of finely triturated particles of ice are taken in the hand and squeezed together, I seem to understand perfectly why “regelation” takes place:- You have drained or squeezed away all the perfect water from the mass, & the molecules of plastic ice ceasing to receive heat from the perfect water [which is operating a minute fusion at the surface of each particle without communicating the smallest quantity of heat to its interior]⁴ the condition of the Ice becomes that of more or less hard Ice not being in contact with perfect water, & this is what is called regelation.

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I had last the pleasure of seeing you at Greenwich in Oct 1851⁵. Since the end of November in that year I have been more or less of an Invalid - at times severely ill - which will account for my comparative inactivity in matters of Science. I trust that your health is good & will long continue so.

Yours sincerely | J.D. Forbes.