324 Of the Propagation of Heat 



in cooling down to that temperature as much Heat as 

 would melt ^\-^ or -^^ of its weight of ice ; the water, 

 therefore, which is cooled from the temperature of 40° 

 to that of 32°, if it be 35 feet deep, will give off as much 

 Heat in being so cooled as would melt a covering of ice 

 1 feet thick. 



But this even is not all ; for as the particles of water 

 on being cooled at the surface would, in consequence of 

 the increase of their specific gravity on parting with a 

 portion of their Heat, immediately descend to the bot- 

 tom, the greatest part of the Heat accumulated during 

 the summer in the earth on which the water reposes 

 would be carried off and lost before the water began to 

 freeze ; and when ice was once formed, its thickness 

 would increase with great rapidity, and would continue 

 increasing during the whole winter ; and it seems very 

 probable, that, in climates which are now temperate, the 

 water in the large lakes would be frozen to such a depth 

 in the course of a severe winter that the Heat of the 

 ensuing summer would not be sufficient to thaw them ; 

 and should this once happen, the following winter could 

 hardly fail to change the whole mass of its waters to one 

 solid body of ice, which never more could recover its 

 liquid form, but must remain immovable till the end of 

 time. 



In the month of February, after a frost which had 

 lasted a month, the temperature of the air being 38°, M. 

 de Saussure found the temperature of the water of the 

 Lake of Geneva, at the surface, at 41°, and at the depth 

 of 1000 feet at 40°. Had the frost continued but a little 

 longer, ice would have been formed.; but had the con- 

 stitution of water been such that the whole mass of that 

 fluid in the lake must have been cooled down to the 



