32 GLACIERS 



A certain moderation in the manufacture is held to be 

 correct, giving the snowball a firm crust, but one which 

 can easily break on the face of the opponent at whom it 

 is thrown, thus allowing the still powdery interior lightly 

 to overwhelm him. 



This property of snow viz. that its particles become, 

 as it were, fused together so as to form a continuous 

 mass of ice when it is squeezed (that is, subjected to 

 pressure) has been carefully examined. The snow par- 

 ticles seem at first sight to behave as though they 

 were viscid or " sticky " in fact, as powdered wax or 

 resin would behave. Yet they are not really viscid at all, 

 but consist of loose crystals of ice, small but hard, and 

 with no tendency to " flow " or soften. Their binding 

 property is found to be due to the fact that pressure lowers 

 the degree of heat, as registered by a thermometer, at 

 which ice melts. The same lowering of the melting-point 

 by pressure has been observed in other bodies which 

 expand when solidifying for instance, sulphur and 

 paraffin. In ordinary circumstances ice melts and becomes 

 water at the temperature registered as 32 deg. on the 

 Fahrenheit scale or zero on the Centigrade scale. A 

 pressure equal to a weight of 2000 Ib. on the square inch 

 of surface lowers the melting-point of ice by I deg. Centi- 

 grade. A very much smaller pressure has its due propor- 

 tional effect, and lowers the melting-point a little. So 

 that merely squeezing powdered ice in the hand or in a 

 squeeze-mould causes it to melt a little and even at the 

 great degree of cold (sometimes experienced in the winter 

 on the Continent, but rarely in England) of 1 8 deg. below 

 zero Centigrade, which is very nearly equal to zero 

 Fahrenheit, a French experimenter has, by applying to 

 ice a pressure (a weight) of several thousand pounds to 

 the square inch, converted it into water. It is, of course, 

 obvious that when ice is caused to melt ever so little by 



