THE EARTH. 14-7 



air, which, after being kept for some time, will 

 be seen to separate. 



Spring water is next in point of purity. This, 

 according to Dr Halley, is collected from the air 

 itself; which being sated with water, and coming 

 to be condensed by the evening's cold, is driven 

 against the tops of the mountains, where being 

 condensed and collected, it trickles down by the 

 sides into the cavities of the earth ; and running 

 for a while under-ground, bubbles up in fountains 

 upon the plain. This having made but a short 

 circulation, has generally had no long time to 

 dissolve or imbibe any foreign substances by the 

 way. 



River water is generally more foul than the 

 former. Wherever the stream flows, it receives a 

 tincture from its channel. Plants, minerals, and 

 animals, all contribute to add to its impurities ; 

 so that such as live at the mouths of great rivers 

 are generally subject to all those disorders which 

 contaminated and unwholesome waters are known 

 to produce. Of all the river water in the world, 

 that of the Indus and the Thames are said to be 

 the most light and wholesome. 



The most impure fresh water that we know, is 

 that of stagnated pools and lakes, which, in sum- 

 mer, may be more properly considered as a jelly 

 of floating insects, than a collection of water. In 

 this, millions of little reptiles, undisturbed by any 

 current, which might crush their frames to pieces, 

 breed and engender. The whole teems with 

 shapeless life, and only grows more fruitful by 

 increasing putrefaction. 



