THE EARTH. 73 



H. ii well known to contain a large mixture of salt and bitumen. On 

 the contrary, those waters which are lightest, have the fewest dissolu- 

 tions floating in them ; and may, therefore, be the most useful for all 

 the purposes of life. But, after all, though much has been said upon 

 this subject, and although waters have been weighed with great assi- 

 duity, to determine their degree of salubrity, yet neither this, nor their 

 curdling with soap, nor any other philosophical standard whatsoever, 

 will answer the purposes of true information. Experience alone ought 

 to determine the useful or noxious qualities of every spring ; and ex- 

 jerience assures us, that different kinds of water are adapted to dif- 

 ferent constitutions. An incontestible proof of this, are the many 

 medicinal springs throughout the world, whose peculiar benefits are 

 known to the natives of their respective countries. These are of va- 

 rious kinds, according to the different minerals with which they are 

 impregnated ; hot, saline, sulphureous, bituminous, and oily. But the 

 account of these will come most properly under that of the several 

 minerals by which they are produced. 



After all, therefore, we must be contented with but an impure mix- 

 ture for our daily beverage. And yet, perhaps, this very mixture 

 may often be more serviceable to our health than that of a purer 

 kind. We know that it is so with regard to vegetables : and why not, 

 also, in general, to man ? Be this as it will, if we are desirous of hav- 

 ing water in its greatest purity, we are ordered, by the curious in this 

 particular, to distil it from snow, gathered upon the tops of the highest 

 mountains, and to take none but the outer and superficial part there- 

 of. This we must be satisfied to call pure water ; but even this is far 

 short of the pure unmixed philosophical element ; which, in reality, 

 is no where to be found. 



As water is thus mixed with foreign matter, and often the reposi- 

 tory of minute animals, or vegetable seeds, we need not be surprised 

 that, when carried to sea, it is always found to putrefy. But we must 

 not suppose that it is the element itself which thus grows putrid and 

 offensive, but the substances with which it is impregnated. It is true, 

 the utmost precautions are taken to destroy all vegetable and animal 

 substances that may have previously been lodged in it, by boiling; 

 but, notwithstanding this, there are some that will stiil survive the opera- 

 tion, and others that find their way during the lime of its stowage. 

 Seamen, therefore, assure us, that their water is generally found to 

 putrefy twice, at least, and sometimes three times in a long voyage. 

 In about a month after it has been at sea, when the bung is taken out 

 of the cask, it sends up a noisome and dangerous vapour, which would 

 take fire upon the application of a candle.* The whole body of the 

 water then is found replete with little worm-like insects, that float, 

 with great briskness, through all its parts. These generally live for 

 about a couple of days ; and then dying, by depositing their spoils, 

 for a while increase the putrefaction. After a time, the heavier 

 parts o f these sinking to the bottom, the lighter float, in a scum, at the 

 top ; and this is what mariners call, the water's purging itself. Thens 

 $ still, however, another race of insects, which are bred, very proba- 



* Phil. Trans, vol. v. part ii. p. 71. 



