Prof. Reusch on some Properties of Ice. 



193 



I have thus in different experiments, in 

 which the distance S S' was 46 to 80 

 millims., observed bendings of 6 to 8 

 millims. Once, indeed, I was able to 

 bend a thin 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 millimetre. 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, 21 

 for the length S S', 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 



b i 



Our values are, for example, A = 690 grms. ; b = 10 millims. ; 

 h = 3 millims. ; 21 = 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 equi- 

 valent 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 homogeneous 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, pro- 

 vided that the temperature of the ice 

 and of the air be below 0° C. Obviously the knife acts in this 



Phil Mag. S. 4. Vol. 27. No. 181. March 1864. O 



