98 LAKES. 



especially if it be but little elevated above the sea, and 

 the land around it be high. The latter circumstance 

 is a certain indication of depth ; and when that extends 

 to a hundred fathoms or so, the water, instead of being 

 covered with ice, even in the longest and most severe 

 winters, does not cool nearly to the freezing-point. 

 Strange stories have been told of lakes that have this 

 property : their waters have been said to be impreg- 

 nated with substances, which, at the same time that they 

 defy the frost, act upon those who drink them. These 

 have been alleged of some of the Scottish lakes that 

 pour their limpid waters iceless into the sea; while 

 all the shallow parts of them are frozen to a consider- 

 able thickness. But there is no need for any admixture 

 to prevent the congealation ; that is the necessary 

 result of the depth, and of a well-known property of 

 water. The greatest density of that fluid is at about 

 forty-two degrees of Fahrenheit ; and until this degree 

 of cold is imparted to the whole volume of the water, 

 of course no ice can be formed on the surface. The 

 cooling process is, in deep water, a very slow one ; as 

 the instant that a pellicle on the surface becomes 

 heavier than the rest, it sinks and exposes a new one. 

 When the water has cooled so far as to become sta- 

 tionary, the action of wind upon the surface furthers 

 the cooling; but even with that assistance the very 

 deep lakes are never frozen. The winter of 1807-8 

 was one of uncommon length and severity ; and yet 

 instead of any ice forming upon Loch Ness, (probably 

 the deepest lake, and most uniformly deep, in the 

 United Kingdom,) the river that flows from it was 

 several degrees above freezing, and only a few slight 



