Vol. III. No. 50. 



THE AGRICULTURAL NEWS. 



87 



WINDMILLS. 



The following infurination on windmills is taken 

 from King's Flii/sics of A(jrleidture : — 



If wo except horse-power and that of cattle, there is no 

 toriu of motor whieli has I>een so generally or so widely used 

 on the farm as the windmill, and its use is daily increasing, 

 especially now since all parts are made of steel, well galvanized 

 to protect them from rust, and their relative efficiency has 

 been increased. 



WORK TO WHICH THE WINDMILL IS ADAPTED. 



It nuist not be understood that a windmill is well suited 

 to furnish power for any and all kinds of farm woik, if only 

 it is made large enough. On the contrary, it i.s only adapted 

 to certain lines where the work done can be accumulated at 

 times when the wind is favourable, such as pumping water 

 for stock and for the supply of the house, if only a suitably 

 placed reservoir of sufficient cajiacity is provided ; for 

 grinding grain for stock, and for wood sawing. 



WIND PEESSUEE. 



The pressure which the wind may exert upon a surface 

 depends primarily upon (1) its weight per cubic foot, (2) its 

 velocity, and (3) the angle at which it strikes the surface. 



ABILITY OF WIND TO DO WORK. 



The work which wind can do depends upon the amount 

 which passes through a given windmill per minute and the 

 pressure which it exerts. But as the pressure varies with 

 the .square of the velocity, and the quantity passing the mill 

 varies directly as the velocity, the theoretic working cai)acity 

 of the wind must increase as the cubes of the wind velocity. 



Perry regards it approximately correct to state that a 

 1 2-foot windmill in a 5-mile wind may develop ~~ of a horse- 

 power, and the figures in the last line in the talsle aliove are 

 his. 



RELATION OF DIAMETER OF WHEEL TO ITS EFFICIENCY. 



In increasing the horse-power of an engine it is not usually 

 necessary to increase its weight and strength much more than 

 in proi)ortion to the increase of power which is to be 

 developed, but in the case of two wind wheels, having the 

 same type of construction, the one which is to develop double 

 the horse-power must have a strength of resistance practically 

 eifht times as great in order to withstand the highest 

 wind pressure.s to which it is liable to be sulyected. This is 

 so because doubling the diameter of the wheel not only 

 makes the surface of wind pressure four-fold, but at the same 

 time carries the centre of pressure farther from the axis of 

 the wheel, causing it to act upon a longer lever arm. But to 

 increase the strength of resistance of the wheel eight-fold 

 makes it necessary to build it much heavier and this detracts 

 from its relative efficiency. 



Resides this, with wheels of large diameter there are 



much greater differences in the wind pressure on the different 

 parts of the wind sails, because the actual velocity of the 

 sails increases with the distance of their points from the 

 centre of the wheel. But the angular velocity must l>e the 

 same in all parts of the sail, and this causes the wind sail to 

 be forced around away from the wind passing through the 

 wheel with very different velocities, and this difference 

 reduces the relative efficiency, so that large windmills of like 

 pattern do not increase the available horse-power as much as 

 the size is increased. 



AMOUNT OF WORK DONE BY A WINDMILL IN PUMPINi; WATER. 



We have measured the amount of water which was 

 pumped during one entire year by a 16-foot geared windmill. 

 This mill was provided with three pumps arranged so as to 

 lift water 12-85 feet whenever there was wind enough to 

 enable it to do any work. When the wind was lightest it 

 was given the pump of smallest capacity, when stronger the 

 one of next size, when still stronger both together ; the third 

 pump being used onlj' in the very highest winds. 



The smallest amount of water lifted 10 feet high, in ten 

 days, was enough to cover 9-87 acres I inch deep, and this 

 occurred from July 28 to August 7, at the time when water 

 for irrigation is most needed. The largest amount pumped 

 was enough to cover 75-73 acres I inch deep. 



A WINDMILL IN GRINDING FEED. 



aiming to measure the amount of 



AMOUNT OF WORK DONE BY 



Another set of trial 

 feed which may be ground with a 12-foot geared windmill, 

 was made at the Wisconsin Experiment Station, and using 

 the observed amounts of corn ground under a wide range of 

 wind velocities and the observed hourly wind velocitie.s, as 

 recorded for the punqiing exi)erinient, the amount of feed 

 which could have been ground, had it been fed automatically 

 and kept running continuously, has been computed and given 

 in the table which follows: — 



Table showing the amount of corn which could have 

 been ground by a 12-foot aermotor windmill during the 

 year, from ilarch 6, 1897, to March 6, 1898, with all winds 

 from 9 miles to 30 miles per hour. 



The total footing of this table .shows that the mill 

 might have ground an average of about 75 bushels of ccrn 

 per day for the entire year, but this figure would represent 

 the maximum amount of «'ork possible. The minimum 

 could hardly have been less than one-third of this amount. 



