where the power is required to obtain the desired fall. Occasionally water power is available in the form of a natural waterfall, and then it is simply necessary to guide the water in a tube or channel to the motor. Sometimes the velocity only of the flowing stream is employed for working the motor, the head in that case being already converted into kinetic energy.

The preceding table gives the water powers which have notably enhanced the industrial development of the country.

In this table the hiatus from 1861 to 1866 is accounted for by the stagnation of industrial enterprise due to the Civil War. In recent years the possibility of transforming water power into electrical energy and its transmission to distant points has aided greatly in promoting the development of water-power enterprises of great magnitude. The Great Falls, the Sault Ste. Marie, the Nigara, the Ogden, and the Mechanicsville developments are notable examples of such water-power electric plants. In each of these cases the water power operates turbines or water wheels which drive dynamos.

BIBLIOGRAPHY. A number of authoritative treatises on water-power development are available. Frizell, Water Power (New York, 1901), is a comprehensive general treatise on all phases of the subject. Bodmer, Hydraulic Motors, Turbines, and Pressure Engines (New York, 1889), is an elaborate technical and descriptive treatise on water motors of all kinds. Merriman, Treatise on Hydraulics (New York, 1900), is a general treatise on hydraulics, including water motors of various kinds. Descriptions of plants will be found in the volumes of Engineering News (New York, current). See DYNAMO-ELECTRIC MACHINERY; TURBINE; WATER WHEEL; HYDRAULIC

ENGINE.

WATER-PROOFING. The coating of arti cles made of textile fabrics, paper, and other substances, so as to render them impervious to water. Besides the treatment of fabrics with a solution of rubber, various preparations are used, such as a mixture of beeswax and yellow rosin in boiled oil. Fabrics may also be rendered waterproof by thoroughly impregnating them with a solution of soap and then dipping them into a solution of alum. Paraffin finds extensive use for the purpose, and articles of various kinds, including leather, and even wood, are made waterproof by keeping them for a time in hot molten paraffin. Several varnishes, too, are used for rendering articles water-proof.

WATER PURIFICATION. The art of removing any objectionable matter from water so as to render it safe for domestic consumption and fit for industrial uses. The objectionable qualities are in the nature of pathogenic bacteria; inert organic matter liable to give rise to offense or injury; turbidity and suspended matters generally; color, taste, and odor; hardness and iron. (See WATER-WORKS, paragraph on Quality.) The principal means of purification are sedimentation, which clarifies water and removes a portion of the bacteria; coagulation, an aid to both sedimentation and filtration; aëration, which removes odor and may supplement filtration; filtration, which removes bacteria and reduces inert organic matter, turbidity, and color; and various

chemical processes for getting rid of either iron or hardness.

SEDIMENTATION is effected by either bringing water to rest or passing it very slowly through shallow reservoirs or basins. The first is called the intermittent and the second the continuous system of sedimentation. The force of gravity carries down some of the clay and silt which compose turbidity. The degree of clarification effected depends upon the size and specific gravity of the particles and the length of time afforded for sedimentation. Some waters are notably improved in a few hours; others are still turbid after a number of days. Partly through the action of gravity, and partly through entanglement with the other suspended matter, a considerable percentage of bacterial reduction is effected by sedimentation. Where bacterial purification, rather than clarification, is the object, sedimentation alone is insufficient, but it may be a great aid to filtration. Storage reservoirs afford more or less sedimentation and bacterial reduction, depending upon both their size as compared with the daily draught and the character of the water. The design and construction of settling reservoirs does not differ from that of other reservoirs, except in the relative shallowness of the former, the arrangement of the inlets and outlets, and the provisions made for removing the deposits of mud from their bottom. In continuous-flow basins having a number of compartments the water generally passes from one section to another in a thin sheet over a long weir. This insures the drawing off of the upper and clearest layer, minimizes the disturbance of water in the successive basins, and may provide aëration of value. If aëration is desired and the levels permit it there may be a series of steps between each weir and the next basin. Two or more compartments are usually necessary, so one may be at rest while the other is being filled; but where the constant-flow system is used for water containing but little sediment one basin may do. Provision must be made for drawing the water down as quietly as possible to a level well above the deposit of sediment, so as to avoid disturbing the latter. The bottoms of settling reservoirs should slope to some common point, where connection should be made with a pipe for flushing out the mud when the reservoir is cleaned. The mud is often loosened by means of water under pressure, thrown from a hose, much as in hydraulic mining.

COAGULATION is effected by introducing a chemical, generally sulphate of alumina, into water. The substance is broken up into alumina and sulphuric acid. The latter unites with the lime or magnesia in the water and is thereby rendered harmless. The alumina thus set free is transformed into hydrate of alumina, a white, flaky, gelatinous substance, which coagulates the or ganic matter in the water and entangles the bacteria. The agent and the impurities are deposited in the settling basin or are removed from the water by filtration. It is essential that the water be sufficiently alkaline to decompose the sulphate of alumina, and that plenty of time be allowed for coagulation. If deficiencies in alkalinity are periodic, as in times of heavy floods, they may be made good by adding lime to the water. The time element is secured by providing basins or reservoirs of proper capacity.

AERATION is accomplished by forcing air into the water requiring treatment, by discharging water over weirs, or by means of fountains. In a few American cities stored water of surface origin is treated with compressed air delivered into the reservoir through perforated pipes. It is claimed that this practice has been very ef fective in preventing organic growths that give rise to bad tastes and odors. Aëration is also used to precipitate iron before filtration, as mentioned farther on. As a rule, aëration is merely supplementary to other processes, making good a deficiency of oxygen. Where water is high in organic matter any amount of aëration which is economically applicable is insufficient for its removal. The process has little or no effect upon the bacterial contents, and is directly opposed to removal of the latter by sedimentation.

FILTRATION plants are divided into slow sand and mechanical or rapid, according to the rate of filtration and the methods of cleaning the filters. The filtering material in either case is generally sand. Slow sand filters are beds of sand, supported on gravel, and provided with underdrains, the whole being inclosed in a watertight basin or basins. The water is admitted on the top of the bed, percolates through the pores of the filtering material, is collected by the underdrains, and then passed to a clear water reservoir or to the consumer. Each bed has an area of one acre or less. The rates of filtration range from 2,000,000 to 5,000,000 gallons per acre per day, according to the character of the water and the fineness of the sand. The filtering sand is commonly two to four feet deep and rests on one to two feet of gravel. The latter is placed in layers, increasing in size toward the bottom until stones as large as hens' eggs are found. The underdrains are four inches and upward in diameter, of either clay, tile, or vitrified pipe. Automatic devices are employed to regulate the rate of filtration. When the head reaches a maximum fixed by theory and experience to suit the local conditions, ranging from three to six feet, one or more beds are thrown out of use for cleaning. The water is drained down to a point somewhat below the level of the top of the bed, and a thin layer of fouled sand is removed by broad shovels. This is washed immediately or else allowed to accumulate for washing at intervals. The washed sand is not replaced until the thickness of the sand bed has been greatly reduced, oftentimes to as little as 12 inches. This is made possible by the fact that the bulk of the work is done in a very thin upper layer of the bed, sometimes not more than one-eighth of an inch deep. The sand is washed (1) by playing hose upon it and allowing the sand and water to flow together through a long flume; (2) by means of running water in a revolving eylinder, provided with arms, or a screw; and, (3) what is more common in America, by a series of hoppers and ejectors. In the latter process the sand is thrown into a wooden or steel hopper, in the bottom of which is placed an ejector. The jet of water carries the sand up with it to the top of another ejector, where the dirty water is drawn off. The process is continued until the sand is clean. Slow sand filtration removes practically all the bacteria and suspended organic matter, a considerable amount of organic matter in solution, more or less turbidity, and a relatively

lieved that the pathogenic germs succumb more rapidly than the harmless water bacteria, which comprise the great majority of those present, so if the total bacterial reduction be sufficiently high the water is considered perfectly safe. If the water to be treated is very turbid it will clog slow sand filters so rapidly that keeping them clean becomes an economic and even physical impossibility. In such cases slow sand filtration is supplemented by sedimentation. If the two processes combined are inadequate, without too great an outlay for settling basins and filter beds of large area, then coagulation may be employed. In such cases it is the practice, at least in America, to substitute mechanical filtration, which almost invariably includes both coagulation and filtration, and frequently sedimentation as well. In very cold climates it is essential to the best sanitary and economic results that the filter beds be covered as a protection against frost and ice. Masonry vaulting is employed for this purpose.

MECHANICAL FILTRATION is, first of all, a straining process, in which the natural capabilities of the filtering medium are aided by coagulation. The gelatinous coagulating material, combined with the more or less sticky organic matters in the water, and with the finely divided clay and silt, form a layer on the surface of the filter and for a greater or less extent on the sides of each sand grain. Thus the effectiveness of the strainer is greatly increased by the reduction in the interstitial passages and by its adhesive qualities. After a comparatively short period, ranging from say two days to twelve hours, the filter becomes clogged. The impurities penetrate the whole mass, so all the filtering material must be washed. This is done by the simple mechanical process of reversing the flow of water through the filter, so it passes upward from the bottom. The dirty water is wasted at the top. Prior to or in connection with the reversed flow the sand is loosened by means of power-driven revolving rakes, gradually lowered into the filtering material. In place of the rakes, compressed air, admitted from the bottom, is used in some mechanical filters. The filter sand is supported on a false bottom, in which are placed the pipes for collecting the filtered and admitting the wash water. Strainers of perforated metal plates or wire netting give the water access to and permit it to flow from these pipes. The coagulant is

an average of 6,463,000 gallons of water per day was treated, at a cost of $1.66 per 1,000,000 gallons for filtration alone, and $4.52 for pumping to the settling basins, cleaning the latter, filtration and laboratory expenses. The $1.66 of expense for filtration alone was divided as follows: Scraping sand from beds, 24 cents; wheeling out sand, 42 cents; replacing sand, 32 cents; incidentals, 13 cents; lost time, 10 cents. The bacterial reduction was about 99 per cent. Practically all of the turbidity was removed and the color was reduced by 24 per cent.

The first mechanical filter connected with a municipal water supply was put in operation at Raritan, N. J., in 1882, by the Somerville Water Company, which supplies Raritan and Somerville. No coagulant was used. In March, 1883, John W. Hyatt patented a filter of the same general type as the one erected at Raritan. In February, 1884, Isaiah S. Hyatt, a brother of John, patented a system of coagulation and filtration combined. These and other patents granted to the Hyatt brothers formed the basis of the Hyatt and later on the New York mechanical filters. Rivals appeared in the market from time to time and much litigation ensued. The latter was confined chiefly to the use of a coagulant. In 1897 the United States Circuit Court of Ap peals, notwithstanding much expert and other testimony designed to show the prior use of coagulating materials coincident with filtration, declared the Hyatt patent valid. The patent expired early in 1901.

For a number of years the use of mechanical filters was confined almost wholly to the production of a bright, clear water. Very little disinterested evidence was available to show their efficiency in this respect and practically none bearing on their bacterial efficiency. In 1893-94 experiments on a small scale were made under the direction of Edmund B. Weston, at Providence, R. I., which indicated that mechanical filters would remove a high percentage of bacteria. In 1895-07 more extensive investigations, on a large scale, were made at Louisville, Ky., with Mr. George W. Fuller in charge. Mr. Fuller's report on these investigations (see bibliography) marked an era in water purification. It showed that a water as turbid as the Ohio, and with the large number of bacteria sometimes carried by that stream, could be rendered thoroughly acceptable by means of sedimentation, coagulation, and mechanical filtration combined. IRON REMOVAL is accomplished most frequently by simple aëration to precipitate the iron, followed by filtration for its removal. If aëration is not sufficient to effect precipitation a chemical may be employed, like milk of lime where the iron is in the form of a sulphate. The few iron removal plants built in the United States up to the middle of 1901 were located on or very near the North Atlantic seacoast, to treat water from wells.

WATER SOFTENING has been employed but rarely in the United States, and then chiefly for supplies to the boilers of manufacturing plants or locomotives. The pioneer water-softening process, and one that is still largely used, was invented and patented by Prof. Thomas Clark, of Aberdeen, Scotland, about 1841. In the simplest form of this process, lime water, or milk of lime, is thoroughly mixed with the water

to be treated. After twelve to twenty-four hours' subsidence the water is so drawn off as to leave the precipitate behind. Modifications of the Clark system include a variety of settling and filtering devices. The process as described will remove only temporary hardness, or carbonate of lime or magnesia. Permanent hardness, caused by the sulphates of lime and magnesia, may be removed or reduced by using carbonate of soda as a precipitate, but the process is too expensive for general use.

DISTILLATION, owing to its high cost, is practicable only for small quantities of water under special conditions. It is used largely at artificial ice plants (see REFRIGERATION) and is sometimes used to freshen sea water. In addition, it is used in connection with various industrial arts. It consists simply in evaporating water in stills by means of heat and subsequently condensing the steam. The heat given off in cooling, in the best large plants, is utilized to aid in raising the water to the boiling point. The process clarifies as well as sterilizes water. Boiling, in any convenient way, is a very cheap and thoroughly effective way of sterilizing water used for household purposes. Both distilled and boiled water must be aërated, or it will be very flat and unpleasant to the taste.

HOUSEHOLD FILTERS, with the exception of a very few kinds, had better be avoided whenever it is feared that there are pathogenic bacteria in the water. There are numerous household filters which are more or less useful as strainers for the removal of mud, and some of the very finegrained filter tubes do good bacterial work if properly cleaned and sterilized at intervals.

BIBLIOGRAPHY. Fuertes, Water Filtration Works (New York, 1901), treats of the practical details of design and construction; Hazen, The Filtration of Public Water Supplies (3d ed., New York, 1900), devoted chiefly to slow sand filtration; Hill, The Purification of Public Water Supplies (New York, 1898), a comprehensive general discussion, giving the relation between water pollution and typhoid fever; Collet, Water Softening and Purification (London, 1895); Kirkwood, Report on the Filtration of River Waters (New York, 1869), largely descriptive and chiefly of historic value; Fuller, Report on the Purification of the Ohio River Water at Louisville, Ky. (New York, 1898), a detailed description of exhaustive experiments with mechanical filters; see also reports of the Massachusetts State Board of Health, 1887 to date, and special reports on experiments at Providence, R. I., Pittsburg, Pa., Cincinnati, Ohio, Washington, D. C., and New Orleans, La. See also FILTRATION and WATERWORKS, and the references to general works in latter article.

WATER RAM. See HYDRAULIC RAM.

WATER-RAT. A large vole (Microtus amphibius), eight and one-half inches in length of head and body and reddish brown in general color, which is numerous throughout Europe. It is closely related in structure and habits to the voles and American meadow-mice, and has similar habits, except that it is more aquatic and diurnal than other members of the genus. It is one of the most familiar of British mammals and typical of the Muridæ.

WATER RIGHTS. A general expression to describe the legal power of using or of controlling the use of the water of flowing streams, ponds, lakes, and of the sea. These rights are numerous and varied in character, but may be generally classified as (1) natural rights, (2) easements, (3) customary rights, and (4) public rights. Strictly speaking, this classification has to do only with private waters, those, namely, whether flowing or stationary, which occupy land subject to private ownership. By the common law the bed of the sea and of tidal waters generally (technically described as 'navigable' waters) is not subject to private ownership, but belongs to the State-in England to the Crown; in the United States to the people of the several States-and is open to public use for all proper purposes (as navigation, fishing, bathing, etc.) without restriction. But wherever waters ordinarily public have become subjected to private ownership, the nature of the proprietary right so gained and the extent to which it is limited by rights of user vested either in the public or in other private citizens become proper subjects of inquiry, just as in the case of waters originally and inherently private. (See RIPARIAN RIGHTS; RIVERS.) Even waters strictly public, however, may be subject to private rights which to a certain extent limit the public right of user above referred to as the rights of access of landing, mooring, and wharfing out, enjoyed by an abutting or riparian owner on a navigable river.

It is of the essence of the doctrine of water rights that the water itself is, in our legal system, not deemed to be capable of ownership. It is true that water collected in cisterns, artificial ponds, etc., the water held in marshy or spongy ground, even the water percolating through the soil or flowing in undefined channels on the surface or underground, is regarded as a part of the earth, and to all intents and purposes as belonging to the owner of the land. Wherefore a landowner may drain his land, or may collect the water therein in wells or cisterns, and may make any use he pleases of it, even though in so doing he cuts off his neighbor's supply of surface drainage or of percolating waters which feed the latter's well or stream. But there is no such thing as the ownership of running streams.

Every landowner has a natural right to the use and enjoyment of the watercourse which flows through his land. It is not acquired by grant or prescription, like an easement, nor can it be alienated apart from the land, nor is it, like an easement, extinguished by non-user or abandonment, nor by unity of possession.' It exists jure naturæ, as an incident to the land, and passes with the land upon the alienation of the latter in whole or in part. It includes the use of the water for all proper purposes-for watering stock, for irrigation, for power, for fishing, and navigation, and for drainage-but such use is strictly limited by the right of every other riparian proprietor to make a similar use thereof. Conversely, the right is infringed by any act-such as diverting, fouling, detaining, or damming back the water, or by draining into itwhich inflicts actual damage or excessive inconvenience. (See RIPARIAN RIGHTS.) A riparian proprietor has a right to a steady flow of the watercourse without material alteration, and

the right is not limited to the main stream, but extends to all contributing streams and springs actually connected therewith, but not to percolating or surface waters not flowing in a defined channel. But a stream flowing in a welldefined channel underground is equally subject to the law of user, above outlined, as is a surface stream. The infringement of riparian rights is a nuisance, remediable by an action for dam ages and by injunction, and, in a proper case, by direct abatement of the nuisance.

By far the most numerous class of water rights are those which come under the description of easements. They include such wellknown easements as drainage, or the right of discharging water upon another's land, the right to take water by a pipe, ditch, or otherwise, from another's land, and the right to flood another's land by damming back a running stream upon it. To these may be added, for convenience, the rights (properly described as profits a prendre rather than as easements) to take ice from the pond of another, to fish in his stream or trout pond. Like other rights of this character (sometimes comprehensively grouped as servitudes, or rights in alieno solo), these may be acquired by grant or prescription and may be lost by release or abandonment. See EASEMENT.

CUSTOMARY WATER RIGHTS are not of frequent occurrence. They consist in the right of a community (as the inhabitants of a town or village), based on immemorial usage, to take water from a private spring or stream or to water cattle at such spring or stream. Rights of this character are not favored in the United States and can hardly be said to exist here, though they are of ancient standing in English law. See CrsTOM.

PUBLIC WATER RIGHTS, or the right of the public at large to use and enjoy private waters, may exist either in waters naturally private, as in non-navigable streams, or in waters which have become subjected to private ownership, as occasionally happens in the seashore or in navigable streams. It is a general rule of the common law that a private stream which is adapted to navigation, even though it be only for floating logs, is subject to the public use for that purpose. This right of the public is strictly limited, however, and does not extend to the taking of fish or cutting ice, or even of landing, but only to the purpose of passing and repassing in a suitable boat, or, as said above, of floating logs at appropriate seasons of the year. The right of fishing, in particular, is an incident of the ownership of the bed of a stream or pond, and no length of user will vest that right in a community or in the public at large. The only exception to this rule appears in the rights enjoyed by the public in the seashore in the rare cases where the latter has become private prop erty. The public ownership of the seashore, i.e. of the strip between low and high water mark to which reference was made above, may be divested by grant from the Crown in England. by legislative act or charter in the United States, in favor of a private individual. In a few of the United States, indeed (Maine, New Hampshire, Massachusetts, and Virginia), the owner of the upland owns the shore. But in all these cases the private owner takes the shore subject to certain immemorial rights of the pub