474 



tions are applied to the ice as distinguished from the water, the theory 

 does not apply in any precise way to determine the conditions of the 

 melting of the ice, or of its growth by the freezing of the adjacent 

 water to its surface ; and I expressed the hope that I might subse- 

 quently communicate to the Society some further developments of 

 the subject. 



On following up various considerations which had then occurred 

 to me, I soon formed positively the opinion that any stresses what- 

 ever y tending to change the form of a piece of ice in ice-cold water 

 (whether these stresses be of the nature of pressures or tensions, that 

 is pushes or pulls, and whether they be in one direction alone, or in 

 more directions than one), must impart to the ice a tendency to melt 

 away, and to give out its cold, which will tend to generate, from the 

 surrounding water, an equivalent quantity of ice free from the 

 applied stresses. I came also to the more general inference that 

 stresses tending to change the form of any crystals in the saturated 

 solutions from which they have been crystallized must give them a 

 tendency to dissolve away, and to generate, in substitution for them- 

 selves, other crystals free from the applied stresses or any equivalent 

 stresses. . In the month of May last, I tested this inference by ap- 

 plying stresses to crystals of common salt in water saturated with 

 salt dissolved from the crystals themselves ; and found the crystals 

 to give way gradually, with a plastic yielding, like the yielding of 

 wet snow, but very much slower. The crystals, with the brine in 

 which they were immersed, were, in the first set of experiments, 

 placed in a glass tube, like a test-tube, and a glass piston, or ram- 

 mer, fitting the tube loosely, so as not to be water-tight, was placed 

 on the top of the salt which lay like fine sand in the bottom, and the 

 piston was loaded with weights. The piston went on descending 

 from day to day through spaces, which, though small, and though 

 diminishing as the crystals became more compacted against one 

 auother, were still distinctly visible. When the rate of descent 

 became very slow, I added more weights, and found that the rate of 

 descent increased, as was to be expected. 1 afterwards procured a 

 strong brass cylinder with a loosely fitted, not water-tight piston, or 

 rammer, and in this I subjected crystals of common salt in their 

 saturated brine to very heavy stresses, and thus compressed them 

 rapidly and easily into a hard mass like rock-salt. The top surface 



