WATER. 



ing the diameter of the wheel. If the wlieel, for inftance, 

 is only 6 feet diameter, its circumference will be 18.8 

 feet, and its floats will move at the rate of 18.8 feet in 

 a fecond, the double of which is 37.6 feet per fecond, 

 which anfwers to a head of water 22 feet high. The dia- 

 meter of the water-wheel, however, ihould never be lefs than 

 6 or 7 feet, becaufe the float -boards change their direiftion 

 fo rapidly, in confequence of their proximity to the centre, 

 that they will not receive the full aAiou of the water, be- 

 caufe it afts in a perpendicular direction to the float -board 

 only for a moment. 'Hence there will be a certain height 

 of the fall, beneath which the Ample horizontal wheel can- 

 not be employed ; and beyond that, wheel-work mud be 

 introduced to obtain the requiflte velocity for' the mill- 

 ftones. 



In the provinces of Guienne and Languedoc, in France, 

 another fpecies of horizontal wheel is employed for turning 

 machinery. It confifts of an inverted cone, with I'piral 

 float-boards of a curvilineal form winding round its furtace. 

 The wheel moves on a vertical axis in a pit or well of ma- 

 fonry, to which it is exaiftly fitted, like a coffee-mill in its 

 box. It is driven chiefly by the impulfe of the water, con- 

 veyed by a fpout or canal in a ftream, which ilrikes the ob- 

 lique float-boards ; and when the water has fpent its impul- 

 five force, it defcends along the fpiral float-boards, and con- 

 tinues to aft by its weight till it reaches the bottom, where 

 it is carried oflF by a canal. The idea of this m.achine is in- 

 genious. The jet of water, being firft apphed to the upper 

 or laro-eft; part of the cone, ftrikes the float-boards at the 

 part where they move with the greatell velocity, in confe- 

 quence of their being on the largeft radius ; but as the w.-iter 

 lofes its velocity, in confequence of the motion it has im- 

 parted to the wheel, it defcends in the cone, and afts upon 

 the floats lower down, where, the radius being lefs, the 

 floats move more flowly, and are therefore better adapted 

 to receive the aftion of the water with its diminiftied ve- 

 locity. 



M. Mannoury Dedot's horizontal Watcr-Whecl, rvhtch 



he calls Danaide This receives the impulfe of the water in 



a diflerent manner from any which we have defcribcd, and 

 is defcribed in a report to the IniHtute of France in 18 13. 

 The water-wheel is fixed in a horizontal pofition upon a 

 vertical axis, and fupported upon the pivots thereof, fo as 

 to be capable of turning round. It is not in reality a wheel, 

 but a hollow cylinder or drum capable of containing water ; 

 it is open at top, and united to the axis in the centre of the 

 circular plane, which forms the bottom. Within this drum, 

 and concentric with it, a folid cylinder is fixed ; it is of lefs 

 dimenfions than the drum itfelf, and occupies fuch portion 

 of the content of the drum as to reduce the open part which 

 can contain water to a hollow ring or circular trough, open 

 at top, and of a confiderable depth, but only a few inches 

 in width. The depth is defcribed as being nearly as great 

 as the diameter of the wheel. 



The water coming from an elevated refervoir, is pro- 

 jefted in jets from one or more pipes into this annular fpace 

 which furrounds the rim of the wheel. Thefe pipes defcend 

 in an inchned direftion, till they are nearly on a level with 

 the furface of the water in the annular fpace ; and the ex- 

 tremities turn horizontally, fo as to projeft the jet horizon- 

 tally, and in the direftion of tangents to the mean circum- 

 ference of the water contained in the annular fpace. 



Suppofe this fpace whicli furrounds the wheel is fuU of 

 water, then the ftream iffuing from the jet caufes the wheel 

 to turn round upon its axis, becaufe it takes hold or aCts 

 upon the water in the annular fpace, and tends to give the 

 water a circulr,ting motion within the annular fpace ; but the 



fridtion, or refiftance, which the water would find in fuch 

 circulation, caufes the wheel to turn round with the water, 

 unlefs the load on the wheel, or refillance to its motion, is 

 too great. 



The water which is continually thrown into the wheel 

 efcapes from the annular fpace by paifages which proceed 

 from the bottom thereof to the centre of the wheel ; and 

 there are openings at the centre, whei-e the water can drop 

 out below. To form the paflages for this purpofe, the folid 

 cylinder which is fixed in the centre of the hollow drum is 

 of lefs depth than the other, and leaves a fpace between the 

 bottom of the foUd and the bottom of the hollow, which 

 is divided into compartments by diaphragms fixed upon the 

 bottom of the trough, and proceeding like radii from the 

 circumference to a central hole in the bottom of the trough, 

 which is left open to allow the water to efcape. The report 

 ftates, that the velocity with which the water iflues from 

 the jets makes the machine move round its axis ; and this 

 motion accelerates by degrees, till the velocity of the water 

 in the annular fpace equals that of the water from the re- 

 fervoir, fo that no fenfible fliock is perceived of the afiluent 

 water upon that which is contained in the machine. The 

 motion of the wheel is regular, becaufe the aftion is con- 

 tinual ; but in the cafe of other water-wheels, where the 

 water ilrikes againd float-boards, fuch boards muft necef- 

 farily be of a determinate number, and the motion muft be 

 given to the wheel by a fucceflion of impulfes, as the floats 

 arrive before the ftream. We might indeed fuppofe a wheel 

 with an infinite number of floats, but it would then amount 

 to a plain cylindrical or flat furface, upon which the water 

 would not take fufficient hold to produce any fenfible effort 

 to turn it round. 



Now in M. Dedot's wheel, in place of float-boards, the 

 rim of the wheel is clothed with water, which is capable of 

 being afted upon by the water ifluing from the jets. This 

 aftion tends to put the water in the annular fpace in motion, 

 and to carry the wheel along with it, by the adhefion it 

 muft naturally have to the fides of the channel which con- 

 tains it. The velocity of the wlieel will be in proportion to 

 the refinance that the load makes to its motion. 



The circular motion of the wheel communicates a centri- 

 fugal force to the water contained in the annular cavity of 

 its rim, which caufes it to prefs againft the outermoft fide 

 of the channel. This centrifugal force afts equally upon 

 the water contained in the compartments at the bottom of 

 the faid rim ; but its aftion diminilhes as the water ap- 

 proaches the centre. 



The whole mals of water is then animated by two op- 

 pofite forces, vie. gravity and the centrifugal force. The 

 firft tends to make the water run out at the hole in the bot- 

 tom of the wheel at the centre, and the fecond to drive the 

 water from that hole. 



To thefe two aftions are joined a third, -c'lz. friftion or 

 refiftance, which afts an important and Angular part ; and 

 in this machine the friftion of the water produces its powers 

 of aftion, while in moft other machines it always diminiflies 

 their powers. The effeft in this machine v^'ould be nothing, 

 were it not for the refiftance which the water finds oppofed 

 to its free circulation in the annular fpace round the rim of 

 the wheel. 



By the combination of thefe three forces there ought to 

 refult a more or lefs rapid flow of water from the hole m the 

 centre at the bottom of the wheel ; and the flower this water 

 ifl"ues, the greater will be the effcftive power of the machine 

 for producing the ufeful eff'eft for which it is deftined. 



The moving power in this machine, hke all others, is the 

 weight of the water which runs into the wheel, muhiplicd 



by 



