NATURAL THEOLOGY. 201 



will remain stationary, and the cold wind or air will 

 soon reduce it to the state of ice. The time necessary 

 for this circulation to he completed, must depend on 

 the depth of the water ; and in deep pieces of water, 

 it is sufficiently long to ensure them from being fro- 

 zen over, unless the cold should be continued for 

 a considerable period. 



To this provision we are indebted for the use of 

 our wells, fountains, and navigable waters in cold 

 weather. They would otherwise be closed up with 

 the first frosty night. The whole fact is one of 

 modern discovery, Dr. Johnson was led to doubt that 

 a small but very deep lake in the highlands of Scot- 

 land, was always open in the hardest winters, while 

 other lakes in the neighborhood were frozen over. 

 If the fact were true, he thought the phenomenon 

 must be owing to the water being unusually sheltered. 



" For where a wide surface," he observes, " is 

 expose d to the full influence of a freezing atmos- 

 phere, I know not why the depth should keep it 

 open. " The difficulty to his mind of conceiving 

 how depth should protect the surface, may still fur- 

 ther impress us with the wisdom of the arrangement 

 by which the effect is produced. 



Without fire, all substances would be converted 

 into one solid mass ; fire being the principle of fluid- 

 ity in water and every other liquid in nature. The 

 very air itself would become solid. Fire is the 

 universal instrument of all the arts and all the neces- 

 saries of life ; and here we are called to admire, that 

 fire and light, in the absence of the sun, are obtain- 



