14 Transactions of the Canadian Institute. [Vol. IX. 



62.4 lbs., while a cubic foot of ice at approximately the same temperature 

 weighs 57.2 lbs. A cubic foot of ice will, therefore, float with its upper 

 surface an inch above the water and will support a weight of 5.2 lbs, 

 before it sinks, and a square foot of ice an inch thick will support a weight 

 of .43 lbs. Like other solids, it contracts with decrease of temperature, 

 the linear coefl&cient of expansion varying from .00005 to .00002 or from 

 3->^ to I ->^ inches per mile for each degree F. 



At the end of autumn as the days become rapidly shorter and colder 

 with the approach of winter, the temperature of the water in the lakes 

 gradually lowers until about the beginning of November it has fallen to 

 freezing point and ice begins to form around the shores where the con- 

 vection currents can carry the heat quickly up and down through the shal- 

 low water and the earth or stones at the bottom can be cooled by radiation 

 into the air. 



At the same time the moisture in the air, which, during the summer, 

 periodically descends to the earth in the form of rain, now begins to fall 

 in the form of snow, and as the snow falls into the lakes part of it remains 

 unmelted in the cold water and adheres or freezes to the edge of the shore 

 ice. Every cold day or night the shore ice becomes thicker by the freezing 

 of additional particles to it from below, as the heat is abstracted from the 

 water by conduction through the ice, and at the same time its edge extends 

 farther and farther into the lake until it completely covers the water. In 

 this way a smooth covering of ice may be formed over the lake. On the 

 other hand a period of very cold weather may suddenly cause the forma- 

 tion of a sheet of ice several inches in thickness over the whole lake. 



On some of the large lakes, just after they have been frozen over, 

 one of the heavy storms, so common in the autumn and early winter, 

 may arise, and the wind and waves may break the ice into irregular masses 

 and fragments, drive them towards the shore, or pile them up against it. 

 At the same time, however, some of the first-formed ice will remain frozen 

 fast to the shore and form an efficient protection to it. Thus the frag- 

 ments of ice broken up by the storms in the early part of the winter have 

 very little influence in displacing the sand and boulders which compose 

 the shore, though they may throw up tree-trunks and floating masses of 

 timber high up over it. 



These storms are often followed by cold, calm weather and during 

 this cold spell the broken ice will be frozen into a rough, irregular covering. 

 Such a rough refrozen sheet of ice may very often be found on many of 

 the larger northern Canadian lakes. 



