In a number of instances of this, perhaps one of the most striking is the Millbank Prison. The prisoners used to suffer from a variety of diseases, one of them being typhoid fever. This they got from water supplied by simply drawing water out of the Thames. Since that practice has been discontinued only three cases have oocurred, and one at least of these was brought into the prison.

If you read the reports of the Government inspectors upon the places where epidemics of this disease have occurred they all tell the same tale over and over again -polluted water.

Ordinary diarrhoea, too, is frequently caused by it, while diphtheria and sore throat, so frequently produced by breathing foul air, have been traced by some observers to the use of impure water for drinking. .

Now, a word or two about the sources of water. Certain accidental sources of water occur. For instance, drinking water has been occasionally obtained out at sea by hanging up blankets which absorb the dew. Melted snow and ice are used in some countries, but the water obtained is not aerated sufficiently, and consequently is bad for digestion, although exceedingly pure.

Bain is the indirect source of all our water supply, and rain-water, when collected away from towns, is very pure soft water; it is therefore advisable to collect.

T rain-water in country places even for domestic use, and this course is a very good one when there is an epidemic of cholera or typhoid fever. Rain-water, however, collected in and near towns is very impure, almost invariably, from the impurities contained in the air of the towns. This has been especially pointed out by Dr. Angus Smith, who examined rain-water collected in various places.

Rain collected half a mile from the extreme southwest of Manchester, although the wind was blowing from the west, after it had been allowed to clear itself of suspended matters, contained more than two and a half grains of organic matter in a gallon, and was, moreover, obviously impure. It becomes clear, therefore, that rain-water in towns, and for some distance around them, is not pure for drinking purposes.

Shallow well-waters are very liable to be impure, and in towns are almost always impure on account of the percolation of foul matters through the surrounding ground, and are, therefore, unfit for drinking. This becomes a very serious thing when we consider what a large number of our towns are supplied by well-waters.

Water derived from artesian wells, that is to say, from wells made by boring down through a series of strata, and ultimately through an impervious stratum into water-bearing rocks below it, afford a very large supply of, generally speaking, very pure and wholesome water; at any Tate water which has not been contaminated by foul matters, so that these wells, which are really supplied with water which has fallen on distant hills, and percolated through the rocks, form an exception, and some of the best water in London is supplied by means of artesian wells.

Spring waters vary very much in the mineral matters which they contain in solution, and they vary according to the kind of rocks from which they come. They are very frequently hard water, but otherwise generally very pure,

Eiver water is very much softer than spring water, but is very frequently largely contaminated with foul organic matter. The towns look upon rivers as outlets for their sewage, and this arises from the fact that the drains which were originally constructed to drain the towns convey the sewage into the rivers, which of course renders them unfit sources for water supply.

But it has been stated that rivers, to a certain extent, purify themselves by flowing, and, in fact, that they purify themselves enough to become a proper source of water supply. There is no doubt that putres-cible organic matters are oxidised and rendered harmless in running water, but there is no evidence to show that the poisons of specific diseases are destroyed in this way, and so water that has been once rendered impure ought not to be used for domestic purposes.

Lakes, especially in mountainous countries, afford a very large source of exceedingly pure water, and you have seen the result of supplying one of our large towns, viz., Glasgow, by means of the soft water from a lake.

A word or two about the connection of water with soils.

Waters that come from surface soils are almost invariably impure. So generally are those from loose sand and soft sandstones.

Waters that come from clay soils are generally hard waters, and contain sulphate of lime in solution, and therefore are objectionable, and they also contain large quantities of organic matter in solution.

Waters that come from the chalk and limestone formations are very hard waters, but otherwise are naturally very pure waters; and waters that come from the granitic rocks are, as a rule, soft, and very pure.

Water that comes from soils containing much magnesia produces swelling of the thyroid gland, called goitre, or "Derbyshire Heck." In a few parts of England, in parts of France and Switzerland, and in some other countries, this disease has been traced to drinking very hard waters, and - especially those containing magnesian salts.

How is water to be supplied to places? The best plan of supplying it is, as the ancient Romans did, to go to a considerable distance from a place and find water which has not been contaminated, and bring that water to the place where it is wanted.

In the year 92 after Christ, Frontinus, the Roman engineer, described the aqueducts bringing water from various distances to Rome. They brought waters of different degrees of purity, and Frontinus tells us that the purest waters were used for drinking purposes, and the less pure waters for washing the streets, and for the various other purposes for which pure water was not necessary.

One of these aqueducts brought water for fifty-four miles. Some of them have been repaired from time to time, and still supply the city of Rome with water. And if you go to Rome to-day the first thing that will surprise you is the immense abundance of pure water they have there, and that immense quantity of pure water is brought by some of the aqueducts made by the ancient Romans. They brought spring water from a distance, collected it in reservoirs, let the suspended matters settle, and then distributed the water by pipes to the different parts of the city. They constructed aqueducts not merely for Rome, but for many other great Roman cities. We have been told that the Romans did not understand the first principles of hydrostatics because they did not use inverted syphons for the aqueducts which supplied Rome. They understood them well, for when they had to traverse deep valleys, as at Lyons, they took the water across by means of inverted syphons, and they used precautions which would perfectly astonish you if I had time to tell you about them.