angle. At the junction of each pair of troughs are placed wooden valves to prevent the return of water. This balance is suspended at its upper end on a level with the irrigating ditch, and is caused to oscillate about this as a center, much as does a pendulum, the motion being produced by a couple of men pulling on ropes. The lower ends of the troughs dip into the stream from which the water is to be lifted, and at every oscillation each series of troughs empties its water into that immediately above, until it is finally lifted to the summit of the balance, whence it is discharged into the irrigating ditch. Irrigating water is now being extensively pumped by windmills in various portions of the West, notably in the San Joaquin Valley of California, in Kansas, Nebraska, and the Dakotas, and elsewhere on the Great Plains east of the Rocky Mountains. Until recently windmills have been most extensively employed for pumping water for domestic use, but as water supplies for irrigation have become scarcer, and as practical farmers have come to appreciate the value of irrigation, they have in seeking new water supplies resorted quite extensively to windmills as motive powers for pumping water. The chief objection to windmills for this purpose is that they are dependent upon the force and regularity of wind for their operation, and as a result they do not urnish as steady and reliable a power as do water, steam, and other agents. This objection is, however, not serious on the Great Plains between the Rocky Mountains and the Mississippi River, especially if storage reservoirs are employed as an adjunct to the mills, for in that region there is, throughout most seasons, a sufficiently steady and powerful wind to keep the wind wheels constantly turning. In other portions of the West the winds are less certain in their action, and may fail the farmer at the very time when he is most in need of a water supply. Windmills are too frequently employed to pump water for irrigation either from the uncertain supplies derived from drive wells or without the aid of a storage tank or reservoir in which to retain the surplus pumped at such times as it is not utilized in irrigation. As a result the supplies which they furnish are insufficient and unsteady, and this has led to their condemnation. The fault in such cases has not been with the mill but with the user. In order to obtain good results from windmills they should not be used where the wind is uncertain and shifting, or in connection with a poor pump, or where a water supply equal to their full pumping capacity is not available; and they should invariably be supplemented by an ample storage reservoir. The wind may blow at any time during the twenty-four hours, and is no more likely to blow in the daytime than at night, when water is not used in irrigating the fields. It is also likely to be as active at seasons when irrigation is not in progress and during the late winter and spring months as when water is being run upon the fields. For security, therefore, and in order to irrigate a reasonable area from a pump of given capacity, ample storage room should be provided for the water which can be pumped during several weeks. This storage room may be obtained by using one of the various forms of elevated wooden tanks supplied by windmill makers; or, better, if the windmill can be located at a high point on the farm an artificial reservoir may be constructed of earth at this point and be suitably lined with earth puddle or asphaltum. It should, if possible, be sheltered from the sun by a roof, so as to decrease losses by evaporation. Such a storage reservoir can easily be given sufficient capacity to retain a much larger volume of water than can economically be stored in a wooden tank. The amount of work which a windmill will perform depends on the force and steadiness of the wind, the size of the wind wheel, its design and construction, and its location. An average wind velocity of not less than 6 miles per hour is required to drive a windmill, and, on an average, winds exceeding this velocity are to be had during eight hours per day; hence, about two-thirds of the total wind movement is available for work. According to reports of the United States Weather Bureau, the average wind movement of the entire country is about 6,000 miles per month, or over 8 miles per hour. These averages are somewhat exceeded in Dakota, where the hourly velocity is from 10 to 12 miles, as it is in Nebraska, Kansas, and neighboring States, while they are too great for some other portions of the arid West. The following table gives roughly the force of the wind for ordinary velocities: Table II, which is derived from Mr. A. R. Wolff's treatise on the windmill,1 and is based on scattered data of actual performances, shows the capacity of a windmill having various diameters of wheels with an assumed average velocity of wind of 16 miles per hour and working eight hours per day. According to Mr. Wolff's estimate, the cost of operating a windmill for a 25-foot lift, including interest on first cost and charges for maintenance, ranges from cent per hour for a 10-foot wheel to 2 cents for a 16-foot wheel and 44 cents for a 25-foot wheel. From an inspection of the foregoing, it is evident that the windmill is one of the most economical of motive powers. Its operation calls for no expense for fuel and little for attendance or repairs. In comparison with it the steam engine requires large expenditures for fuel, repairs, and attendance, and nearly all water motors call for heavy outlay in providing and maintaining their water supply as well as for repairs and attendance. It appears that on the average the economy of a windmill is at least one and one-half times that of a steam pump, while it has an additional economy over the latter because of the attendance and repairs demanded by the steam boiler. Extensive experiments with a view to obtaining a comparison of the efficiency of various windmills have been recently made by Mr. J. A. Griffiths in Australia. The highest net efficiency observed in Mr. Griffiths's experiments with the wind blowing 7 miles per hour was 25 per cent. Table III gives the results of his experiments for the five American-made wind wheels tested.2 'The Windmill as a Prime Mover, by Alfred R. Wolff, M. E., John Wiley & Sons, New York, 1890, 161 pp. 2 Windmills for raising water, John Alfred Griffiths: Minutes of Proceedings of the Institution of Civil Engineers, Vol. CXIX, London, 1895, pp. 321–343. TABLE III.-Capacities and efficiencies of several windmills. Average continuous horsepower developed per 100 square feet. Average quantity of water lifted per hour... .gallons.. per cent... .28 1.11 .71 1.59 .78 .72 |