WATER. 



by the elevation the refervoir lias above the bottom of the 

 wheel, or orifice from which it iffues in quitting tlie fame ; 

 but the ufeful mechanical effeft is Rated to be equal to that 

 produft, diminilhed by half the force which the water re- 

 tains, when it flows out at the orifice below, and quits the 

 machine. 



In order to afcertain, by direft experiment, the magni- 

 tude of this effect, Meflrs. Prony and Carnot fixed a cord 

 to the axis of the machine, which pafling over a pulley, 

 raifed a weight by the motion of the machine. By this 

 means the effeft was found to be -/nths of the power, and 

 often approached -/„Vths, without reckoning the friftion of 

 the pulleys, which has nothing to do with the effedl. 



We cannot help fufpedling fome millaice in thefe experi- 

 ments, or in the llatement of them, but think the machine 

 deferves a trial ; and if it (hould produce near the refult 

 above ftated, it would be a moll valuable addition to our 

 means of employing falls of water ; and its fimplicity would 

 be a great recommendation, particularly for corn-mills, be- 

 caufe the perpendicular axis is immediately adapted for that 

 purpofe, without any wheel-work. 



Horizontal Mill ivith oblique Vanes In Belidor's Archi- 



tefture Hydraulique he defcribes a ditferent form of Ijori- 

 7.ontal mill. The wheel is a circular rim, and the radii or 

 arms are all oblique vanes or floats, precifely the fame as the 

 common fmoke-jack. This wheel is placed horizontally in 

 a well, to which it is exaftly fitted, but the rim of the wheel 

 does not touch the circular wall of the well. The axis of the 

 wheel afccnds upwards into the mill-lioufe, and the fpindle 

 of the mill-ftone is fixed into it. A horizontal arch-way is 

 condufted to the well fideways, and above the part where the 

 wheel is fituated. This arch conveys the water into the 

 well over the wheel ; and beneath the wheel there is a fimilar 

 horizontal arch to carry away the water, after it has palled 

 through the wheel, that is, in the fpaces between its vanes 

 or floats. The weight of the water prelTes upon them in a 

 perpendicular direftion, ami tlie planes of thefe floats being 

 all inclined to the horizon, the action of the prelTure tends 

 to turn the wheel round on its axis, by the fame aftion as 

 the fmoke upon the vanes of a jack, or like a wind-mill. 



The water is fupplied in Inch a body through the upper 

 arch, that the well is always kept full, with a confiderable 

 depth of water preffing upon the wheel ; whilft the lower 

 arch carries away the water fo freely, that it runs awav 

 from beneath the wheel as fail as it can pafs through the 

 vanes of the fame. 



The mill defcribed by Belidor was at Touloufe, and 

 contained a number of fuch wheels in a row, each giving 

 motion to one pair of Hones. 



Horizontal Machines moved by the Readion of Water. — 

 The rcaftion of water, ilfuing horizontally through a fpont 

 or orifice, may be employed to communicate motion to 

 machinery ; and though this principle has not yet been 

 adopted in practice, it appears from theory, and from fome 

 detached experiments .on a fmall Icale, that a given quantity 

 of water, falling through a given iieight, will produce greater 

 elTeAs by its reaftion than by its impulfe. If we fuppofe 

 a vertical pipe of any given height, open at both ends, and 

 that water is poured into it at tiie top, the water will ilTue 

 at the bottom of the pipe with a velocity proportioned in a 

 certain manner to its altitude, becaufe every particle of water 

 which i'lucs is prefied upon and impelled by the weight of 

 all the particles which are above it. Now, fuppofe the 

 pipe bent or curved at the bottom, fo that it will turn the 

 ftreani of water into a horizontal pofition ; in this cafe, the 

 prelfure and force, of which we have fpoken, will be de- 

 fiedted from the vertical direftion to tiie horizontal. Nov.' 



It IS clear that the bent part of the pipe, or fome part of the 

 mtenor furface of the tube oppofite to the orifice, muft fuf- 

 tain all the prefTure which is thus defleaed or tranfmitted ih 

 another diredion ; and if the tube is freely fufpended, it will 

 retreat before this preflTure, and be put in motion. If we 

 fuppofe the tube to have no rcfiftance to motion, then it 

 would receive all the motion of the water, which would not 

 move at all after it in"ued from the orifice, but the orifice 

 and tube would move away from the water. This is an ira- 

 poflTible cafe, and in reality the motion of the effluent water 

 will be divided between the pipe or tube and the iffuing 

 water, in proportion to the rcfiftance with which each is 

 loaded. Another and perhaps more familiar explanation is, 

 that thevvater preffes againil every part of the interior part 

 of the pipe, except againft the orifice or aperture, which is 

 open ; and in confequence, the unbalanced preffure on the 

 part oppofite to the orifice will tend to put the pipe in 

 motion. A llcy-rocket mounts in the air from a fimilar caufe. 



Dr. Barker's mill by the reaction of water was the firft of 

 this kind of machines, and is defcribed by Defaguliers, in 

 1743- I" his Experimental Philofophy, vol. ii. p. 460, he 

 calls it a machine to prove Mr. Parent's propofition experi- 

 mentally, viz. that an under-fliot water-mill does moft work, 

 when the water-wheel moves with only a third part of the 

 natural velocity of the water that drives it. He fays, that 

 Dr. Barker had this thought, and communicated it to him, 

 faying, that it would be an experimental proof of Mr. Pa- 

 rent's propofition ; in confequence of which, Defaguliers 

 made a working model of it, which he ihewed to the Royal 

 Society, and the experiments upon it, at their meeting in 

 1742. 



It confifts of an upright pipe or trunk, communicating 

 with two horizontal branches, hke an inverted T ; thus, J^. 

 This perpendicular pipe is poifed upon a pivot at the lower 

 end, and the upper end is conne£led vvitli the fpindle of the 

 mill-itone, or other machine to which it is to communicate 

 motion. The top of the pipe is formed into a funnel, into 

 which a ftream of water is conduced, and runs down the 

 pipe : the water efcapes through a hole in each of the 

 horizontal arms, which holes are near the ends of the arms, 

 and open in oppofite diredlions, and in fuch a pofition that 

 they will direft the llream of water horizontally, and nearly 

 at right angles to ^he length of the arms. 



Suppofe water to be poured in at the top of tlie tube 

 from tiie fpout, it will then run out by the holes at the ends 

 of the arms, witli a velocity correfponding with the depth 

 of thefe holes beneath the furface of the water in the vertical 

 pipe. The confequence of this mud be, that the arms 

 mull be prefied backwards, for there is no folid furface at 

 the hole on which the lateral preflure of the water can be 

 exerted, while it afts with its full force on the infide of the 

 tube oppofite to ;!ie hole. This unbalanced preffure, afting 

 upon the oppofite fides of botli arm.s, will make the tube 

 and the horizontal ann revolve upon the fpindle as an axis. 



This will be more eafily underllood, if we fuppofe the 

 orifices to be flint up, and confider the prelfure upon a cir- 

 cular inch of the arm oppofite to the orifice, the orifice 

 being of the fame fize. 



The preffure upon this circular inch will be equal to a 

 cylinder of water, whofe bafe is one inch in diameter, and 

 whofe altitude is the height of the fall ; and the fame force 

 is exerted upon the fhut-up orifice. Thefe two preflures 

 being equal, and afting in oppofite direftions, the arm will 

 remain at reft ; hut as foon as the orifice is opened, the 

 water will ilFue with a velocity due to the height of the fall. 

 The preffure of the w.iter upon t! e orifice will now be re- 

 moved, and as the preffure upon the circular inch oppolite 



to 



