ON THE AIB AND WATER OF TOWNS. 77 



and sparkling, as well as dissolving rocks, and making those various solutions 

 which we often find difficult to imitate. At the same time we must infer that 

 the purest water is a great agent in removing the vegetable matter from the 

 soil, in the form of carbonic acid, and that it is not essential that the carbonic 

 acid should rise directly from the soil, or that plants should be placed on the 

 spot to consume it. It has never been the custom to add oxygen to any of 

 the aerated waters ; but although very little is absorbed, it would probably 

 be a very useful imitation of the natural process to add that gas in addition 

 to carbonic acid. 



Rain-water has often been asserted to be the purest of all water, and if 

 falling on siliceous rocks it must still remain pure, as they have very little 

 soluble matter to impart. This may be the case in some districts, but the 

 probability is against it, as rain is a mode of removing impurities from the 

 atmosphere ; and for the large towns in Lancashire, and similar places, there 

 can be no reliance placed on mere rain-water. Collected in a town, we know 

 it to be a nauseous and black liquid ; and when we go a mile from a town it 

 is no less nauseous, although it loses its blackness. This would show that the 

 black soot from chimneys is deposited very near a town, although the soluble 

 substances are carried further ; and it may be observed, that in wet weather 

 the smoke falls more rapidly, from the soot becoming heavy with moisture, 

 as well as from the change of the barometer. Even many miles round a town 

 the rain is unfit for use, without being passed through purifying materials. 

 I have tried it as far as ten miles from Manchester ; and it is probable that it 

 is nowhere free from objection, as it has been found necessary to take means 

 to render it palatable even in agricultural districts. But this same water 

 having passed through sand or rock comes out brilliant and in every respect 

 good, being purified by the natural process. For this reason, as has been 

 often remarked, the water springing out at some depth is much superior to 

 that lying on the surface. 



Even rain-water standing for a time gives indications of organization, which 

 is not the case with deep water. Although the water which does not come 

 from a great depth does contain more organic matter than rain-water, it has 

 gained other advantages sufficient to overbalance that fault ; if, indeed, the 

 small amount of organic matter found in water from sandstone can be looked 

 on as a disadvantage. As the washing of the air seems to be one of the duties 

 of rain, it is not surprising that some mode should be again employed by na- 

 ture to purify the rain. The action of the soil for this purpose seems to be a 

 necessary completion of the process. Dew does not exhibit the same extent 

 of impurities, no doubt arising from the limited space in which it is formed 

 whilst the rain passes through a large extent of air. 



As the use of surface-water has been so highly recommended, I have thought 

 it well to state the valuable qualities of a good filter, and the mode in which 

 I believe the best wiiler is produced. This I believe to be by filtration, which, 

 even more than distillation, removes the organic matter, and more than any 

 known method, improves the taste and the appearance. As the rain-water 

 has washed the air, and the deep well-water has brought with it solutions of 

 degraded rocks to a large extent, both seem objectionable ; and as the surface- 

 water carries along with it matters of all kinds in solution and suspension, 

 according to circumstances, it seems more advisable that the water which has 

 been purified by passing not too deep under the surface should be used, since 

 all the advantages and all the peculiar powers of filtration are found in that 

 portion of the ground. 



