the Appearance of Man on the Earth, 57 



rature can never be replaced by water of a higher tempera- 

 ture, on account of the inferior weight of the latter. Deep lakes 

 exhibit, therefore, this peculiarity, that heat cannot descend 

 downwards, whereas cold may. But as it is impossible for water 

 of an icy temperature to arrive at the bottom of the lake, it 

 follows that the lake cannot be frozen to the bottom. 



Many experiments, made, for instance, in the lakes of Swit- 

 zerland, prove the truth of our theory. On examination, the 

 temperature of their lower regions amounts at all seasons to 

 from 41° Fah. to 43°.2 Fah. The cause why it was never exactly 

 39° Fah., is attributable partly to the internal heat of the earth, 

 partly to the circumstance that water of the temperature of 

 39° Fah. never reaches the bottom without being mixed with 

 some of the warmer particles through which it passes. This 

 temperature of 41° Fah. or 43° Fah. is observed in all the lakes 

 where that of the surrounding atmosphere sinks in winter at 

 least as low as 39° Fah. It is common to all the lakes of the 

 northern and southern countries of Europe ; as, for instance, 

 to the lakes of Sweden, Norway, and Lower Germany, as well 

 as to those of the Alps and of Italy. Hence it is intelligible 

 why the same species of fish are found in lakes belonging to 

 very different climes. The unequal temperature of the atmo- 

 sphere does not in the least affect them. The fish inhabiting 

 the lakes in the north of Sweden swim about in their native 

 element at a depth where the water has constantly the same 

 temperature ; as is, for instance, observed in the Lago di Como, 

 although in winter the atmosphere frequently shows 20° or 30° 

 below 32° Fah., whilst in summer it rises here as many degrees 

 above 32° Fah. It is only during the hot season that the fish 

 betake themselves to the upper regions, in order to deposit 

 their spawn. 



The same providential care which Nature has bestowed on 

 the accommodation of the finny tribe is also discernible in the 

 manner in which she has attended to the comforts of quadru- 

 peds. The organization of each particular class is strictly 

 adapted to the climate and condition of the country assigned 

 to it. The ice bear and the reindeer are confined to the polar 

 regions ; the lion and the leopard to the torrid zone. Misery 

 and death await them should they venture beyond the bounds 



