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it ; that between the ice and the water there is a film varying in 

 local temperature from side to side, which may be called plastic ice, 

 or viscid water ; and that through this film heat must be constantly 

 passing from the water to the ice, and the ice must be wasting away, 

 though the water be what is called ice-cold. 



There is a manifest difficulty in conceiving the possibility of the 

 state of things here described : and I cannot help thinking that 

 Professor Forbes has been himself in some degree sensible of the 

 difficulty ; for in a note of later date by a few months than the paper 

 itself, he amends the expression of his idea by a statement to the 

 effect that if a small quantity of water be enclosed in a cavity in ice, 

 it will undergo a gradual " revelation ; " that is, that the ice will in 

 this case be gradually increased instead of wasted. In reference to 

 the first case, I would ask, What becomes of the cold of the ice, 

 supposing there to be no communication with external objects by 

 which heat might be added to or taken from the water and ice 

 jointly considered ? Does it go into the water and produce viscidity 

 beyond the limit of the assumed thin film of viscid water at the sur- 

 face of the ice ? Precisely a corresponding question may be put re- 

 latively to the second case that of the large quantity of ice enclosing 

 a small quantity of water in which the reverse process is assumed to 

 occur. Next, let an intermediate case be considered that of a me- 

 dium quantity of water in contact with a medium quantity of ice, and 

 in which no heat, nor cold, practically speaking, is communicated to 

 the water or the ice from surrounding objects. This, it is to be ob- 

 served, is no mere theoretical case, but a perfectly feasible one. The 

 result, evidently, if the previously described theories be correct, ought 

 to be that the mixture of ice and water ought to pass into the state 

 of uniform viscidity. Prof. Forbes' s own words distinctly deny the 

 permanence of the water and ice in contact in their two separate 

 states, for he says, " bodies of different temperatures cannot continue 

 so without interaction. The water must give off heat to the ice, but 

 it spends it in an insignificant thaw at the surface, which therefore 

 wastes even though the water be what is called ice-cold.' 9 Now the 

 conclusion arrived it, namely, that a quantity of viscid water could be 

 produced in the manner described, is, I am satisfied, quite contrary to 

 all experience. No person has ever, by any peculiar application of 

 heat to, or withdrawal of heat from, a quantity of water, rendered it 



