WATER. 



preffure of the atmofphere on their upper furface before the 

 air gets admiflion beneath the floats ; but in Befant's wheel 

 this refiftance is greatly diminifhed, as the floats emerge from 

 the ftream in an oblique direftion. The water-wheel is 

 conftrufted in the form of a hollow drum, fo as to refift the 

 admiflion of the water. Although this wheel is much hea- 

 vier than thofe of the common conftruftion, yet it revolves 

 more eafily upon its axis, as the llream has a tendency to 

 make it float. We cannot recommend this wheel, but on 

 the contrary think it one of the w.orft forms, as it tends to 

 increafe that lofs which arifes in all underfliot-wheels from 

 the change of figure which the water muft undergo when it 

 llrikes the float, and we fliould not have mentioned it, but 

 that it has been fo frequently copied and recomnTeuded by 

 different authors. 



HurW.ontal Water- luheels affuated by the Impulfs of Water. 

 — Thefe have been confiderably in ufe on the continent, and 

 defervc our notice from the limplicity of their conftruftion. 

 The wheel is conftrufted in the fame manner as an under- 

 fliot-wheel, having float -boards fixed round its circumference 

 in the form of radii ; it is mounted on a vertical axis, the 

 upper end of which is fixed to the fpindle of the mill-ilone, 

 if the mill is intended to grind corn ; but in fome cafes, it is 

 better to fix a cog-wheel on the upper part of the vertical 

 axis with teeth round its edge, to give motion to trundles 

 or pinions on the fpindles of the mill-ftones, becaufe the 

 floats of the wheel muft always be made to move with a 

 given proportion of the velocity of the water. The wheel- 

 race or water-courfe may be made nearly the fame as for an 

 undcrfliot-wheel, if we fuppofe it laid down in an horizontal 

 pofition ; that is, a trough or channel of mafonry is con- 

 ftrufted in which the wheel works, and the float-boards of 

 the wheel are exaftly fitted to it : at one end of this chan- 

 nel is the aperture or fluice through which the ftream of 

 water ifl"ues, and ftrikes the floats of the wheel fo as to 

 turn It round, and the water pafles forwards and efcapes at the 

 other end of the channel. When the water is dehvered upon 

 the wheel in an horizontal direftion, or perpendicular to its 

 axis, the float -boards fliould be inclined about twenty -five 

 degrees to the plane of the wheel, and the fame number of 

 degrees to the radius, fo that the loweft and outermoft fides 

 of the float-boards may be fartheft up the ftream and be met 

 by the water firft. 



In many cafes, the water-courfe is made inclined to the 

 plane of the wheel in fuch a degree, that the water may ftrike 

 the float-boards perpendicular to their furfaces. 



In the fouthern provinces of France, where horizontal 

 water-wheels are generally employed, the float-boards are 

 made of a curvilineal form fo as to be concave towards the 

 ftream ; they are generally fegments of fpheres, or hollow 

 wooden bowls or ladles fixed on the rim of the wheel : the 

 water, in this cafe, is condufted through a pipe, and pro- 

 jefted in a jet on a direftion a little inclined to the horizon. 

 When the height of water is very confiderable, this is, 

 perhaps, the beft form for the floats, or ladles, as they are 

 called. 



The chevalier de Borda obferves, that in theory a double 

 eff'eft is produced when the float-boards are concave, but that 

 tlieeffcftisdiminifliedin praftice,fromthedifriculty of making 

 the fluid enter, and leave the curve in a proper direftion. 

 Notwithftanding this difficulty, however, and other dcfefts 

 which might be pointed out, horizontal wheels with con- 

 cave float-boards are always fuperior to thofe in which the 

 float-boards have plane furfaces. 



Mr. Smeaton conftrufted a fmall corn-mill with a hori- 

 zontal water-wheel, of which the following are the prin- 

 cipal dimenfions. Fall of water 5 zi feet ; diameter, or 



bore of the nofe-pipe through which the water ifl"ued in 

 a jet to ftrike upon the wheel, li inch ; diameter of the 

 water-wheel 10 feet to the centre' of the floats or ladles, 

 which were twelve in number ; they were made of a concave 

 form, nearly fegments of fpheres, and about 14 inches in 

 diameter ; and fixed round the circumference of the wheel, 

 fo that the planes of the circular rims, or edges of the 

 hollow ladles, were not perpendicular to the plane of the 

 wheel, but inclined thereto in fuch a degree, that the jet of 

 water in"uing from the nofe-pipe at an angle of 2 2 degrees 

 from the horizontal line, would ftrike the floats in the centre 

 and perpendicular to the circular edge of the hollow ; the 

 internal furface of the floats being really fpherical, the water 

 would always ftrike perpendicularly into the concavity of 

 the bowl. The water-wheel axis rofe up perpendicularly 

 into the mill-houfe, and on the top a wheel of 4 feet 8 inches 

 in diameter, and 44 cogs, was fixed for giving motion to the 

 pinions on the axis of the mill-ftones. The largeft pinion 

 of 17 cogs was fixed on the axis of a pair of ftones 4 feet 

 6 inches in diameter, and the fmaller pinion of 1 3 cogs on 

 the axis of a ftone 3 feet 6 inches in diameter. It was 

 not intended to turn both thefe pairs of ftones at the fame 

 time, but it was neceflary to have two pairs for different 

 ufes. 



When this mill moved with a proper velocity to grind 

 to the greateft advantage, if the 4 feet 6 inches ftones were 

 ufed, the water-wheel made 25 revolutions per minute, and 

 the ftones therefore made 65 revolutions per minute, and 

 the float-boards moved with a velocity of 784 feet *^r mi- 

 nute ; but when turning the fmaller mill-ftones of 3 feet 

 6 inches diameter, the water-wheel went beft when it made 

 26 revolutions, and therefore turned the mill-llone 88 turns 

 per minute ; and the velocity of the floats was 816 feet per 

 minute. 



Mr. Smeaton calculated the velocity of the water ifluing 

 from the pipe at 3403 ketper minute, which is the velocity due 

 to a JO feet feet, becaule he allowed the 2^ feet to overcome 

 friftion, and the expenditure of the li inch nofe-pipe at 30 

 cubic teetper minute allowing for friftion. This mill ground 

 one bufhel of wheat per hour, on the average of a great 

 many experiments, now 30 x 50 = 1500 cubic feet, falling 

 one foot per minute. It is found by repeated experiments, 

 that 600 cubic feet falling one foot per minute on a good 

 water-wheel is an ample allowance for grinding a buftiel of 

 wheat, as it may be done by 530 ; hence this fall of water 

 ought to have ground 25 bufliels per hour inftead of one. 

 The mill, however, admits of improvement in making the 

 floats of the wheel move quicker. 



When the mill-ftone of an horizontal mill is fixed on the 

 upper end of the axis of the water-wheel, if the mill-ftone be 

 five feet in diameter, it ftiould never make lefs than fixty turns 

 in a minute, and the wheel muft perform the fame number 

 of revolutions in the fame time ; and in order that the 

 eff'eft may be a maximum, or the greateft poffible, the ve- 

 locity of the current muft be more than double that of the 

 wheel. 



Suppofe the mill-ftone, for example, to be 5 feet dia 

 meter, and the water-wheel 7 feet, it is evident that the 

 mill-ftone and wheel muft at leaft revolve 60 times in a mi- 

 nute ; and fince the circumference of the wheel is 22 feet, 

 the float -boards will move through that fpace in the 60th 

 part of a minute, that is, at the rate of 22 fcot per fecond ; 

 which being doubled, makes the velocity of the water 

 44 feet one fecond, anfwering, as appears from the rule, 

 for the velocity of falling water, to a fall of 30 feet. But 

 if the given fall of water be lefs than 30 feet, we may 

 procure the fame velocity to the mill-ftone, by diminifti- 

 L 3 ing 



