V¥ATEll. 



wheel. To render thr fall of the water eafy, tlie (lope is to 

 be rounded off by a convexity at top and a concavity at 

 bottom, to lead the water from the horizontal to the Hope, 

 and again from tlie flopc without abruptnefs. It is fiip- 

 pofed that the water, iu running down this inchned plane, 

 will acquire the fame velocity as if it had fallen perpen- 

 dicularly through a height equal to the perpendicular 

 height of the flope. 



The diltance through which the water runs horizontally, 

 from the foot of the Hope before it afts upon the wheel, 

 (hould not be lefs than two or three feet, in order that the 

 different portions of the fluid may have obtained an hori- 

 zontal diredtion ; but if this horizontal diftance be much 

 larger, the velocity of the ftream would be diminilhed by its 

 fritlion on the bottom and fides of the water-courl'c. That 

 lefs water may efcape between float-boards and the bottom 

 of the courfe, it (hould be formed into the arch of a circle 

 concentric with the wheel, which fweep fhould be pro- 

 longed, fo as to fupport the water as long as it can att upon 

 the float-boards ; beyond this fweep (hould be a ftep or fall 

 of not much lefs than nine inches with a flope of about 

 45 degrees, that the water having fpent the greater part of 

 its force in impelling the float-boards, may not accumulate 

 below the wheel and retard its motion. After this itep the 

 courfe of difcharge, or tail water-courfe to run off the water 

 from the wheel, (hould be floored with wood or niafonry 

 about 1 6 yards long, having an inch of declivity in every 

 two yards. 



The canal which condudls the water from the courfe of 

 difcharge to join the river again, fliould Hope about four 

 inches in the firft 200 yards, and three inclies in the lecond 

 200 yards, and fo decreafing gradually till it terminates in 

 the river. But if the river to which the water is conveyed, 

 (hould be fubjeft to be fwollen by the rains, fo as to force 

 the water back upon the wheel, the canal mud have a 

 greater dechvity, in order to prevent this from taking 

 place. Henct' it will be evident, that very accurate levelhng 

 is neceflary for the proper formation of the mill-courfe. 

 The tail water-courle ought always to have a very confi- 

 derable breadth, which fhould be greater than that of the 

 wheel-race, or part in which the wheel afts, that the water 

 having room to fpread may have lefs depth. The feftion 

 of the fluid at the point where it ftrikes the wheel (hould be 

 rcftangular, the breadth of the flream having a determinate 

 relation to its depth. If there is a great Itream of water, 

 the breadth fhould be triple the depth ; if there is a mode- 

 rate quantity, the breadth fhould be double the depth ; and 

 if there is very little water, the breadth and the depth fliould 

 be equal. The depth of the water here alluded to is its 

 natural depth, or that which it would have, if it did not 

 meet the float-boards. The effective depth is generally two 

 and a half times the natural depth, and is occaiioned by the 

 impulfe of the water 011 the float -boards, which forces it to 

 fwell, and increafes its atlion upon the wheel. 



As it is of great confequence that none of the water 

 fhould efcape, either below the float-boards or at tlieir 

 fides, without contributing to turn the wheel, the breadth of 

 the float -boards fliould be wider than the fheet of water 

 which llrikes them. The diameter of the water-wheel 

 fhould be as great as pofTible, unlefs fome particular circum- 

 flances in the conflrudtion prevent it ; but ought never to 

 be lefs than feven times the natural depth of tlie llream or 

 thicknefs of the flieet of water, where it meets the float- 

 boards. The wheel will move irregularly, fometimes quick 

 and fometimcs flow, according to the pofltion of the floats 

 with refpcft to the fl;ream ; unlefs the number of float -boards 

 is confiderable, the wheel muft have fo many floats, that 



Vol. XXXVIII. 



two floats will at leafl; be always in the circular fweep at 

 the bottom of the wheel; but in order to remove any 



inequality of motion in the wheel, and prevent the water 

 from efcaping beneath the tips of the float-boards, it fhould 

 have as many float -boards as poffible, without loading it, or 

 weakening the rim on w.hich they are placed. The float- 

 boards fliould not be perpendicular to the rim, or, in other 

 words, a continuation of the radius, but fltould be inclined to 

 the radius ; the water will tlius heap upon the float -boards, and 

 att not only by its impulfe, but alfo by its weight. When 

 the velocity of the ftream is eleven fi;et per fecond, or above 

 this, the inchnation fliould never be lefs than thirty degrees; 

 or v/hen this velocity is K-fs, the inclination fhould diminifli 

 in proportion ; fo that when it is four feet, or under, the 

 inclination fhould be nothing, that is, the float-boards fliould 

 point to the centre of the wheel. 



It is a llrong practical obje&ion to this manner of apply- 

 ing the water to the wheel, that when the water of the river 

 finks in dry weather from a deficiency of water, it would 

 not run over the top of the fall, and the mill could not work 

 at all even if it funk only ten or twelve inches : in like 

 manner, when the water rifes in floods, the water at the top 

 of the fall would become fo deep, as to require fome fhuttle 

 to prevent it from inundating the wheels, at the fame time 

 that the f-tagnant water in the mill race would prevent the 

 wheel from working. Almoil all rivers are fubjeft to 

 floods, and 'often they rife and fall, three, four, fix, and 

 eight feet above their ordinary level in fair weather ; now 

 the water moftly rifes at the tail or difchai-ge of the water 

 as much as the head, and the wheel-race will therefore be 

 full of ilagnant water, which is called tail-water, and ob- 

 ftrufts the motion of the wheel. 



In a ground-fhot wheel, where the water iffues from a 

 fhuttle on a level with the bottom of <he wheel-race, it can 

 always work in dry feafons, as long as the river contains 

 any water, although the power diminifhes almoft to nothing, 

 when the water finks low, and will not rufh out with force 

 from the fliuttle. In floods of .water, this wheel has a 

 greater advantage, hecaufe the depth of head which urges 

 the flowing water is increafed when the water is high, and 

 this makes it drive the tail-water forcibly^ out of the wheel- 

 race, and enable the wheel to work, when a wheel with 

 an inclined fall would infallibly be (lopped. 



Breaft-wheels and overihot-whecls, properly conftrudled, 

 have ftill greater advantages, in clearing themfelves from 

 tail-water, and this is a very important objeft. 



Floating-Mill luith iindeijlM Wheels. — A large floating 

 water-mill, to be worked by the tides or currents, was fta- 

 tioned fome years ago in the river Thames, between London 

 and Blackfriars bridge, by permiffion of the Board of 

 Navigation. Such permiffion having been granted with the 

 view of reducing, if pofBble, the price of flour in the 

 metropolis, and contributing to a con'.lant fupply of that 

 recelfary article of fubfiftence. The fimphcity of this in- 

 vention renders a long defcription fuperfluous, as it confifts 

 in merely applying the force of two large underfliot water- 

 wheels on each fide of a barge, or any other veffel calculated 

 to contain the interior part of the machinery ; the float- 

 boards are difpofed in a proper manner to be afted on by 

 the tide or current, fo as to give the wheels a rotatory motion, 

 ::nd by connefting them with proper machinery, to anfwer 

 tl;'.' purpofes for which the mill is intended. 



Any fliip, brig, (loop, or other veffel, may be ufed for 

 this purpofe, provided it is of fufficient fize to accommo- 

 dr^te the works to be erefted, yet in point of expence it will 

 be better to employ fuch as' are rendered unfit for fea- 

 fervice, 



L "When 



