44 Statistics of the Permanently Diseased. however, includes many suffering from diseases which do not prove fatal, and which tend materially to make this ratio so low. In reference to the permanently diseased, it may be interesting to know the number of the deaf and dumb, blind, idiotic, and lunatic persons in the United Kingdom at the time of taking the census of 1871, and I, therefore, insert the following table, from which it may be learned that in Ireland the ratio of the two first classes of afflicted persons to the population is much higher, and that of the idiotic lower, than in either England or Scotland, whilst the ratio of the insane to the population is higher than in England and lower than in Scotland. Table showing the number of the Deaf and Dumb, Blind, Idiotic, and Lunatic in the United Kingdom in 1871. Deaf and 11518 1 in 1972 2087 1 in 1610 5554 1 in 974 10489 8670 191591 in 1643 WITHIN the last twenty years great attention has been given to the subject of the water supplies of towns, and the chemical examination of water from private wells has of late become very general. During the middle ages almost every European town was supplied with water derived from superficial wells situated within the urban limits. At the present time, although an elaborate system of sewerage works conveys the waste matters of towns into rivers or the ocean, the water of town wells and pumps is often, nay generally, loaded with dangerous organic matter. We may therefore easily imagine how impure must have been the water obtained from town wells in mediaval ages, when the soil was saturated with those waste animal and vegetable matters which in modern times are haply, for the most part, got rid of by subter ranean conduits. In former ages the mortality of towns was frightfully in excess of that of country districts. In many instances the death-rate of a crowded city was more than double that of rural districts situated under the same climatic conditions. Narrow streets, overcrowded and ill-ventilated tenements, defective provision for the removal of effete matters, and personal uncleanliness were prime causes of the shortness of human life in medieval times, indeed, in towns long after that gloomy period of European history had passed away. But a prime factor in the causes of the unhealthiness of towns was the bad water which their wells supplied. When fearful epidemics decimated the inhabitants of cities the cry often arose that the wells were poisoned. This complaint was in general only too true; but the poison in the wells was not put into them designedly-it was derived from the foul drainage of the soil, tainted with the matters thrown out from the bodies of the sick. In former times one of the most active agents in spreading epidemic diseases amongst crowded centres of population was impure potable water. During recent years matters with respect to supplies of water for domestic purposes in town and country appear to be very much reversed. Formerly the citizen, as a rule, was obliged to drink water of a bad or doubtful quality, whilst the denizen of country parts could easily get his draughts of the pure element from crystal spring or sparkling rivulet. Now, the inhabitants of the larger towns are gradually giving up the use of pump water, and are substituting therefor pure water obtained from distant lakes and rivers. On the other hand, owing to various causes, the water used for domestic purposes in the country is not, in general, as pure as it was in the middle ages. In the first place, the rural population has increased, and there is, consequently, more effete animal matter thrown into the soil. Secondly, tillage husbandry, which includes the application of large quantities of manure to the land, has been largely extended. It may be that the potable water in use in country districts is not greatly inferior to that used in the middle ages; but that there is some deterioration in its quality is certain; and this fact is evident, that most of the large towns are now supplied with better water than is usually obtainable in villages and in a large proportion of detached country houses. The ocean is the indirect source of all the water of our rivers and springs. The heat of the sun's rays is continuously distilling the water from the ocean's surface, and converting it into invisible vapour, or gas. The air holds this vapour, or steam, in solution, somewhat in the same way that sugar is dissolved in water, and the warmer the air is, the greater is the quantity of water vapour which it is capable of holding in solution. There are continued currents in the atmosphere, and the air which to-day overlies the ocean may to-morrow be a hundred miles from the sea. When the temperature of air saturated with watery vapour becomes lowered, then its capacity for holding water in solution being dimi 46 Influence of Rocks on Drainage. nished, a portion of that substance is condensed and assumes some liquid or solid form, such as rain, snow, ice, or dew. Mountain tops cool the air, and hence much of the rain that falls descends on the uplands. Of the water derived from this atmospheric source, a small proportion evaporates into the air, and the remainder gradually drains into the ocean, from which, in the progress of time, it will be again converted into vapour. On its way to the sea it gathers itself together-so to speak-and forms rivers. The smallest springs and the largest rivers are produced from drainage water; and wells made by digging deep into the earth intercept a portion of the underground drainage water ere it reaches a river. Our water supplies being directly derived from drainage, it follows that the nature of the rock or soil from which this indispensable fluid is collected exercises some influence upon its composition. In soils there are a great many substances which water is capable of dissolving. The water in the soil usually contains carbonic acid gas, whereby it is enabled to dissolve chalk and other substances which are insoluble in pure water. Most of these substances are used as food by plants; and although they are so soluble in water out of the soil, there is a beautiful provision of Nature which prevents the drainage water from removing them, except in small quantities, from the soil; for otherwise the most fertile land would speedily be deprived of its plant-food and be rendered barren. Drainage water, however, always contains some solid matters dissolved in it, and their amount chiefly depends upon the nature of the rocks which form the drainage area, or catchment basin, as the district yielding the water is termed. The Plutonic, or igneous rocks-granite, syenite, trap, porphyry, &c.afford, with few exceptions, very pure water. The millstone grit yields also very good water, but generally somewhat harder than that obtained from granite and gneiss. In general, the lias (certain mixtures of clays and limestones), limestone, and chalk yield water not equal in purity to that obtained from the granitic rocks, but having a much pleasanter flavour, owing to the large quantity of carbonic acid gas which it holds in solution. This water is usually very hard. The water from dolomite, or magnesian limestone, and rocks containing gypsum resembles the chalk water, but it is not nearly so wholesome, owing to the bad effects which the sulphate of lime (gypsum, or plaster of Paris) produces on the stomach and other organs. The water from sandstones and rich soils under cultivation is generally impure. Surface drainage and subsoil water are occasionally good enough to be used for domestic purposes, but, as a rule, they are to be regarded with suspicion. Marsh water and water contaminated with sewage are extremely dangerous, and should never be used. The well water derived from the drainage of the surface of the ground is not so pure, as a general rule, as that obtained by sinking deep into the earth. The composition of shallow wells constantly varies, whilst that of very deep wells, and especially of the kind termed "artesian," is nearly constant. Lake, River, and Well Water. 47 The drainage of the ground is affected not merely by the geological character of the rocks through which it flows, but also by the density of the population, the state of the water shed, and the provisions for the removal of organic refuse. In every place where a dense population exists, it is almost physically impossible that the surface water which supplies the superficial wells could be pure. In country districts this kind of water is occasionally very pure, owing to the absence of manure, or because the drainage is obtainable from a thin and grass-covered soil. The deeper the well is the greater is the drainage area which supplies it. A shallow well often collects only the drainage of a few hundred square yards; in which case the liquid, not having been subjected to prolonged contact with the purifying clay, is almost certain to contain organic impurities in excess. When making a well these points should be fully considered. If the well be only six or eight feet deep, care must be taken not to have a cesspool or manure heap on any part of the catchment area, for otherwise some oozings from the manure would be sure to get into the well. For this reason, if for no other, liquid manure tanks and cesspools should be so constructed as to prevent the leakage of their contents. They should also be placed as far as possible from the well-an observation which applies with equal force to sewers. A large proportion of the cases of well-water pollution which comes under my notice arises from leakages from sewers. Lake water in these countries is usually very pure; in some of the Welsh lakes I have found little more than 0.001 per cent. of solid matters held in solution. It is, however, owing to its softness, and in summer, relatively high temperature, not so palatable as spring water. The relative values of spring (including well) water and that of rivers is a point difficult to be decided. In many densely populated districts the rivers are so largely polluted with sewage from towns that their waters are inferior to that of the wells. On the other hand, in purely pastoral or agricultural districts the wells are more generally contaminated with organic impurities than the rivers. The motion of the water of rivers, and the action of aquatic plants which grow in them, tend to destroy its organic impuri ties. As a rule, river water is soft, and spring water hard. I have often found the well waters of a district to contain from 50 to 80 grains of solid matters per gallon, whilst the rivers flowing through it held in solution only three or four grains of solid matters per gallon. Sometimes, however, there is a remarkable similarity between the water of a river and that of adjacent wells. This I found to be the case with a spring which supplies the town of Carrickon-Suir, County of Tipperary, with water, its composition being almost identical with that of the river Clareen, as shown in the following table : Composition of Waters used in Carrick-on-Suir. An Imperial Gallon, 70,000 Grains, of each contains: Rain water, caught on the roofs of houses, is in country districts usually very pure; but in towns and populous suburban localities it often contains soot, coal ashes, and various others matters which it meets with in its descent through the air or on the house-tops. The more serious impurities of rain water appear to be the result of the common practice of storing it in uncovered barrels or open cisterns, in situations contiguous to the ash-pit. I have frequently examined the sediment from the rain water stored in suburban houses, and almost invariably found it to contain coal ashes, vegetable refuse, and similar matters. I would, therefore, recommend that as wide a space as possible should separate the ash-pit and water cistern. Water barrels and cisterns and their conduits require to be cleaned very often; and those vessels should be carefully covered, and the water, when required, drawn off by means of a stop-cock. The mouths of wells should be kept covered; and if their sides be built of brick or stone, and cemented on the inside, the water will be kept free from much impure matter. A rainfall of thirty inches per annum delivers 678,000 gallons of water per acre, or about 212 gallons on each square yard. In order, therefore, to estimate the supply of rain water, it is only necessary to ascertain the amount of the rain-fall and the area of the roof or other surface on which it is caught. It has been calculated that one seventy-fourth part of the rainfall would afford sufficient water for all the human beings and lower animals in England; a less proportion would suffice for Ireland. Mr. Bailey Denton, the eminent engineer, has suggested a method of supplying villages and small towns with good water and in sufficient quantities. He proposes to collect in reservoirs all the drainage from the subsoil when it has penetrated to the extent of about four feet. By this operation the land would be deprived of its excess of moisture, and reservoirs of very soft and wholesome water would be collected for the use of the villagers or townsfolk. In the case of a village containing 400 inhabitants, and re |