Water--will It Purify Itself?

Editors of Augüs : How and from what source shall the city of Ann Arbor bo supplied with pure water, ia a question that has boen a matter of diseussion among hnr citizons for a number of years, and up tothis timo with nodefinitoresult. One proposition is to take water from tho river noar McMahon's dam ; anothor, from the river below the town ; ono from small lakts on the west of tho city; and still another from gprings on the south. Wo do not propose here to diacuss the merits of either of these projects, but cali the attention of your readers to the views of J. Lucas, F. O. 8. of the Geological Hurvoy of England, in a work rocently on "Horizontal wells- a new application of geologioal principios to effact the solution of the probleni of supplying Loudon with pure wator." Mr. Luoas's views, it will be kere seen, are greatly at varianee with many celobrated scientists in regard to water purifying itsfilf by exposure. He says : " Mere chemical analyses of waters with and without organio impurities being of Httle use, if unaccorapanied by medical statistics of results following their uae, and organic matter ia water arising as it does from various sources, ome of which may be innocuous and others poisonous, it is probable that we shall never arrive at the exact influence on health of the percentage of organic matter contained in Thames water. That considerable sewage contamination may take place without indioation of its presence by nitrites and nitrates is a fact that deprives chemical analyses of any claim to value as indicationB of the unwholsomeness of water, more especially as the noxious part of sewage exists there in the form of minute germs so small that they are as yet beyond the reach of chemical science ; with microscopic living nisms especiauy, cnemutry is incompetent to deal. It would appear, tierefore, that testing drinking-water is perfectly vseless. We learn that when water is once contaminated with sewago, there is no procesa to which it is afterwards subjected that will effectually remove all that sewage eontamination from the water, and that. though sewage in water may become nearly entirely oxidised, we cannot inform ourselves of the amount that remains. The natural good sense of the greater part of the populution of London who avoid drinking Thames water as much as possible is therefore fully borne out by the investigations of science. Water obtained from permeable strata by means of series of subterraneous galleries is necessarily free from all sewage or drainage contamination, being perfectly flltered by nature; its advantages for drinking purposes over all water obtained by surface collection. and frnm Hvora U. ble to any contamination, are perfectly evident. If, then, a large town requires water supply, and at no great distanoe f rom it there lies a forraation containing alternations of porous and impervious beds which rise above the level of the town, there should be no difficulty in supplying water to it at high pressure on the