WATER. 



the obliquity with which it ftrikes the buckets, and in confe- 

 quence of the lofs of water occalioned by a confiderable 

 quantity of fluid being dalhed over their fides. Indead, 

 therefore, of expeftinjj an increafe of elfeft from the im- 

 pulfe of the water occafioncd by its fall through fome part 

 of the whole height, we fhould caufe it to aft through as 

 much as poflible of this height by its gravity, by making 

 the diameter of the whetl as great as poflible. But a dil- 

 advantage attends even this rule ; for if the water is con- 

 veyed into the buckets with a very fmall velocity, which 

 muft be the cafe when the diameter of the wheel equals the 

 height of the fall, the velocity of the wheel will be re- 

 tarded by the impulfe of the buckets flriking againft. the 

 water, in order to put it in motion, and much power would 

 be loft by the water dafhing over them. In order, there- 

 fore, to avoid all'inconveniences, the diftance of the fpout 

 from the receiving-bucket fhould, in general, be about two 

 or three inches, that the water may be delivered with a velo- 

 city a little greater than that of the wheel ; or, in other 

 words, the diameter of an overfhot-wheel fhould be two or 

 three inches kfs than the greateft height of the fall ; and 

 yet it is no uncommon thing to fee the diameters of thefe 

 wheels fcarcely one-half of that height. In fuch a con- 

 ftruftion, the lofs of power is prodigious. 



It is always dcfirable that the water fhould have fome- 

 what greater velocity, than the circumference of the wheel 

 in coming thereon, othcrwife the wheel will not only be re- 

 tarded by the buckets flriking the water, but thereby dafh- 

 ing a part of it over fo much of the power is loft. 



The velocity that the circumference of the wheel ought 

 to have, will be known by what we fhall fay next, and the 

 depth of column requifite to give the water its proper velo- 

 city, is eafily computed from the rules and tables given in 

 this article, and will be found much lefs than what is gene- 

 rally fuppofed. 



This maxim obliges us to ufe a wheel, whofe diameter is 

 nearly equal to the whole fall ; but we fhall not gain any 

 thing by employing a larger wheel. It is true, we could 

 then apply the water upon a part of the circumference 

 where the weight will aft more perpendicularly to the ra- 

 dius, but we fhould lofe more, by the neceffity of difcharging 

 the water at a greater height from the bottom, becaufe the 

 water, in all cafes, begins to run out of the buckets long 

 before they arrive at the bottom of the wheel. 



Suppofe the buckets of both wheels equally well con- 

 ftrufted in either cafe, whether the wheel is only as high as 

 the fall, or of a greater height, then the heights above the 

 bottom, where they will difcharge the water, will increafe 

 in the proportion of the diameter of the wheel. That we 

 (hall lofe more by this, than we gain by a more direft appli- 

 cation of the weight, is plain without any further reafoning, 

 by taking the extreme cafe, and fuppofing our wheel en- 

 larged to fuch a fize, that the ufelefs part below would be 

 equal to our whole fall. In this cafe, the water would be 

 fpilled from the buckets as foon as it is dehvered into them. 

 AU intermediate cafes, therefore, partake of the imperfec- 

 tion of this. It was the objeft of Mr. Buchanan's bucket- 

 wheel, which we have already defcribed, to avoid this dif- 

 ficulty, and employ a height of fall which bore only a fmall 

 proportion to the whole height of the wheel. This obfer- 

 Tation necefTarily leads us to confider the beft form for the 

 buckets. 



III. On the bejl Form for the Buckets of overjljot Wheelt. — 

 It is impoflible to conftruft the buckets fo that they will re- 

 main completely filled with water till they reach the bottom 

 of the wheel : indeed, if the buckets were formed by par- 

 titions direfted to the axis of the wheel, the whole water 



muft run out by the time they have defcendcd to the levci 

 of the axis ; and, in confequence, there muft be a great- 

 diminution in the mechanical efleft of the wheel. Mill- 

 wrights have, therefore, turned their chief attention to the 

 determination of a form for the buckets which fhall enable 

 them to retain the water through a great portion of the 

 circumference of the wheel. An infpeftion oi^gs. 2 and 3 

 will fhew at once the proper form which has been eftablifhed 

 by long praftice. Thefe are called elbow-buckets, be- 

 caufe each partition is formed by two boards, which are 

 put together with an angle or elbow. The rule for fetting 

 thefe out is, to divide the wheel into the number of buckets 

 it is intended to have ; then take four-fifths of the fpace or 

 interval between two partitions for the depth of the fhroud- 

 ing, that is, the breadth of the circular rings at the fides of 

 the wheel, which form the ends of the buckets, and are 

 called the fhrouds ; whilft the planking, which forms the 

 bottom of all the buckets, is called the fole of the wheel. 

 That board of each partition which is in the direftion of a 

 radius to the wheel, rifes from the fole half the depth of 

 the fhroud ; the other board of the bucket is fo inchned, 

 that its outer end fhall be advanced beyond the line of the 

 next radius-board, if it was produced. 



It is a great advantage to make the partitions of the buckets 

 thin, particularly the edges of the partitions, which will 

 meet and divide the ftream of water flowing upon the wheel ; 

 and if thefe edges are not made fharp, they will fplafli the 

 water about ; the edges are, therefore, finifhed by iron- 

 plate, or it is better to make all the inclined parts of the par- 

 tition of iron-plate. The greater number of buckets, arid 

 the fhaUower they are, the more regularly the wheel will 

 aft. The limits are, that the mouths of the buckets fhall 

 be of fuch width as to allow the air to efcape, at the fame 

 time that the ftream of water flows in ; and alfo that the 

 breadth of the wheel fhall not be extravagantly great, to 

 make its buckets contain as much water as would produce 

 the power required from the wheel. 



The lofs of water, at the lower part of the wheel, will 

 very much depend upon the proportion of water which ii 

 poured into each bucket. It is evident, that if the buckets, 

 of whatever form they are made, were totally filled when at 

 the top of the wheel, they muft begin to fpill the water im- 

 mediately when they departed from that poiltion. But, on 

 the other hand, if only a part of the content of each bucket 

 is filled with water, then it will bear a greater degree of in- 

 clination, and be a longer time before the water will begin 

 to fpill from the bucket. This is a reafon for making large 

 buckets, and filling only a part of their contents. In prac- 

 tice a medium muft be Itruck between thefe contending cir- 

 cumftances, and the wheel will aft to advantage. 



It has been propofed to apply another bend to the parti- 

 tion-boards of each bucket which fhall be beyond the in- 

 clined board that we have defcribed, and fhall be concen- 

 tric with the rim of the wheel, in the fame manner as is 

 reprefented in Mr. Buchanan's wheel, ^^.5. It is true 

 that this form would retain the water from fpilling fdr a 

 longer time, and thus be an advantage ; but it is not favour- 

 able for admitting the water into the buckets when at the 

 top of the wheel. 



The inclined boards, when made as we have defcribed, 

 may be exaftly in the line of the ftream of water, which 

 ifTues from the fpout when it pafTes beneath fuch ftream ; 

 and in this way, if the edge of the inclined board is made 

 thin, there will be as little fplafhing of the water as poffible. 

 But by the addition of another part to the edge of the par- 

 tition, which is concentric to the circle of the wheel, the 

 ftream of water cannot be made to proceed exaftly in the 



line 



