72 A HISTORY OF 



from without. Kircher used to show in his museum, a phiai ol water, 

 that nad been kept for fifty years, hermetically sealed ;* during which 

 it had deposed no sediment, but continued as transparent as when 

 first it was put in. How far, therefore, it may be brought to a state 

 of purity by distillation, is unknown ; but we very well know, that all 

 such water as we every where see, is a bed in which plants, minerals, 

 and animals, are all found confusedly floating together. 



Rain-water, which is a fluid of Nature's own distilling, and which 

 has been raised so high by evaporation, is, nevertheless, a very mixed 

 and impure substance. Exhalations of all kinds, whether salts, sul- 

 phurs, or metals, make a part of its substance, and tend to increase its 

 weight. If we gather the water that falls, after a thunder-clap, in a 

 sultry summer's day, and let it settle, we shall find a real salt sticking 

 at the bottom. . In winter, however, its impure mixtures are fewer, 

 but still may be separated by distillation. But as to that which is 

 generally caught pouring from the tops of houses, it is particularly foul, 

 being impregnated with the smoke of the chimnies, the vapour of the 

 slate or tiles, and with other impurities that birds and animals may 

 have deposited there. Besides, though it should be supposed free 

 from all these, it is mixed with a quantity of 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 underground, 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, generally are 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 is 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 summer, may be more properly considered 

 as a jelly of floating insects, than a collection of water. In this, mil- 

 lions of little reptiles, undisturbed by any current, which might crush 

 their fiames to pieces, breed and engender. The whole teems with 

 shapeless life, and only grows more fruitful by 'increasing putrefac- 

 tion. - 



Of the purity of all these waters, the lightness, and not the trans- 

 parency, ought to be the test. Water may be extremely clear and 

 beautiful to the eye, and yet very much impregnated with mineral 

 narticles. In fact, sea-water is the most transparent of any, and yet 



* Hermetically sealing a ass vessel, means no more than heating the mouth of the phi&l 

 td hot ; and thus when the glass is become pliant, squeezing the mouth to: ether with a f ii 

 of pincers, and then twisting it six or seven times round, which effectually closer it up. 



