XXXIII. On Some Properties of Ice. | By Professor REUSCH of Tübingen. | To John Tyndall, Esq., F.R.S. &c. | Tübingen, Jan. 28, 1864 | (Würtemberg)
Sir,
Your book2 has awakened my interest for that wonderful body ice; and I have devoted the recent cold weather to a more accurate determination of its coefficient of refraction for ordinary and for extraordinary light, as well as to the observation and measurement of the coloured rings of polarized light. In particular your interesting observation upon the layer of snow which sank away from the roof of the greenhouse and curved itself below (page 202), led me to make a direct experiment upon the deformation of ice—an experiment which answered perfectly, and a description of which will perhaps be more interesting to you than to anyone else.
A plate of clean ice, A B, about 100 millims. in length, 12 to 15 millims. in breadth, 3 to 4 millims. in thickness, prepared by sawing and subsequent rubbing with a warm metal plate, is laid in the loops S S of a cotton or silken string which pass above over two pegs, N, N1; a third loop, T, carries a weight of about 200 grms. The temperature of the circumambient space should not much exceed 4° to 6° C. After the lapse of 20 to 30 minutes a bending may be plainly seen, which is at first regular, but afterwards greater in the middle, in consequence of the middle string becoming imbedded in the ice, and of the diameter of the plate being diminished. I have thus in different experiments, in which the distance S S1 was 46 to 80 millims., observed bending of 6 to 8 millims. Once, indeed, I was able to bend a thing lamella of ice between the fingers of both hands.
In one experiment I allowed the ice to break, and measured the dimensions of the surface of fracture as well as I could; the greatest tension and pressure in the outermost layers I found to be = 690 grms. to the square millimeter. It would not be without interest to determine the constants of elasticity and rigidity (Festigkeit) for ice. Putting 2P for the greatest weight in the middle, 2l for the length S S1, b for the (horizontal) breadth, h for the (vertical) thickness of the plate of ice, A for the greatest tension in the outermost layer, we have
Our values are, for example, A = 690 grms.; b = 10 millims.; h = 3 millims.; 2l = 100 millims.; P = 107 grms.; 2P = 214 grms. If about 300 grms. be suspended from the middle, the plate would therefore soon bend, owing to the melting away consequent upon that degree of pressure. I believe that this experiment could be carried out in summer.
It has certainly happened to you, that in sawing through ice, the saw after a short time has ceased to act, the spaces between its teeth becoming filled up with freshly-formed ice, so that it passes along almost without friction. In truth the saw melts through the ice, the heat necessary for that being the equivalent of the work applied to the saw.
The finest plates of ice adapted for optical observations, and about 6 to 8 millims. in thickness, were found in my wash-hand bowl, a tolerably large tin vessel, in which the water (80 millims. in depth) froze during the very cold nights in my bedroom. (River- and spring-ice are always too little homogenous for optical purposes.)
In dividing these precious plates of ice, I soon found that it was necessary to handle them like glass. If the convex blade of a knife be passed over a piece of ice with a certain pressure, a sharp crack will result, and the plate may be broken in the direction of this crack, provided that the temperature of the ice and of the air be below 0° C. Obviously the knife acts in this instance like a diamond, which depresses minute particles of glass, and through the wedge-action of which a progressive linear cracking is produced which renders fracture possible. A mere scratch suffices neither for glass nor for ice. It is worthy of notice that these clear sharp cracks are possible in ice which is in contact with water in a warm room – a proof that ice preserves its brittle character at temperatures lying close to its melting-point. The breaking off at the crack is, on the other hand, no longer possible on account of the regelation in upper part of the crack.
I remain, | Yours truly, | E. REUSCH, | Professor of Natural Philosophy, | Tübingen.
E. Reusch, ‘On some Properties of Ice’, Phil. Mag., 27 (1864), pp. 192–4
RI MS JT/1/R/16
In this translation of Reusch’s letter to Tyndall published in the Phil. Mag., the following passage which began the handwritten letter was omitted: ‘Above all I would like to express my sincere admiration for the chivalrous way that you fought for and continue to fight for the rights & achievements of my friend Dr. Mayer of Heilbronn, even against your own esteemed countrymen. You have done a noble deed in the service of truth and it will bring you blessings. Further, I would like to thank you for the great pleasure it gave me to read your delightful book “Heat, considered…” I do not recall having ever read a book from beginning to end with such satisfaction’ (RI MS JT/1/R/16). Here Reusch was referring to Heat as a Mode of Motion.
Your book: The Glaciers of the Alps.
Please cite as “Tyndall2071,” in Ɛpsilon: The John Tyndall Collection accessed on