HYDRODYNAMICS. 



555 



unhot piece of hard wood, with the flaunch parallel to the 

 ^ Wheel*. ^ horizon, and in that position the arms and rings were 

 "*" v ~"*' trained and bound fast to it. All the grooves for starts 

 or raisers, and buckets, were cut out before it was re- 

 ; t, moved ; first one piece was bolted to the flaunch at a a, 

 and so of the others, leaving the distant openings for 

 the cross bars that reach between each arm and its op- 

 posite arm. These bars, or pieces, were only \ inches 

 square, and were of good beech wood, turned round in 

 the body. They were 10 inches square at each end, in 

 which was fitted a strong nut for a bolt, 1 ', inch thick, 

 to go through t, and connect the two sides together. 



After the arms were trained and fixed right upon the 

 gudgeons, the innermost ring was completed ; the te- 

 nons were trained on the arms first, and the rings, 4^ 

 indies thick and 8 inches deep, put on by keys driven 

 into the mortice. The remaining tenons were then re- 

 duced from 1 j to 1 inch thick, and the outermost ring, 

 only 3 inches thick by 6 inches deep, was firmly wed- 

 ged thereon, and bound fast at the other ends by three 

 strong wooden pins, as at O C ; to the lower ring, the 

 outside of the uppermost and undermost rings are flush, 

 all the additional thickness of the lower ring projecting 

 inside the buckets. 



Some difficulty was found in laying the water pro- 

 perly into the buckets of this wheel, owing to the nar- 

 rowness of the mouths of the buckets, by the high 

 tart or raiser, which was remedied by adopting the 

 following plan. 



The openings in the bottom of the troughing should 

 be of iron, and so distant from each other that the water 

 from them is thrown into two separate buckets. The 

 iron curved parts should also be moveable, to adjust 

 the openings to the quantity of water necessary for the 

 wheel. Unless the bead of water is 12 or 14 inches 

 above these openings, it will be difficult to give it the 

 proper direction into the buckets, especially if the 

 openings are pretty wide for them ; for then it deviates 

 the more down from the line of direction, and tends to 

 retard the wheel, by striking on the outside of the 

 bucket. 



The openings from which the buckets are filled, 

 ought to be 10 inches less in length than the buckets. 

 i. r. 5 inches at each side, otherwise the water is apt to 

 jerk orer on each side of the wheel, as the edge of the 

 bucket passes by. 



The mode of making and fininhing the wheel at 

 C aruide requires very little workmanship, compared 

 tn the usual method ; and any good joiner will do it 

 as well as a mill-wright. The joiner finished Cartside 

 wheel in six or seven weeks. The construction will 

 be better understood from the following reference to 

 the figures. 



Fig. 4. Represents three distinct transverse views. 

 The part marked A, supposes a part of the shrouding 

 in section shewing the pins ; the part marked B, is a 

 section of the wheel through any part of the buckets, 

 and shewing three of the ties, 1, 2, 3, in section. Part 

 C shews the manner in which the exterior ends of the 

 wheel are finished, alio the gudgeons, flaunch, &c. 



Fig 5. Is a longitudinal section of the wheel through 

 one of the arms, shewing the projection of the shroud- 

 ing the manner in which the arms of the wheel are 

 connected together and likewise the manner in which 

 the tie* are connected to the gudgeon. 



Dctcriptio* of Double Overihot Wheel nilh a Chain 

 a/Bucket*. 



When there is a very null supply of water falling 



Owshe* 

 Wheels. 



from a very great head, the overshot wheel which it is 

 necessary to employ is so large and expensive, and so 

 apt to be injured from its unwieldy size, that few per- 

 sons would be disposed to erect one. We have seen overshot 

 at Coalbrook Dale a very excellent overshot wheel, of wheel with 

 about fifty feet in diameter, which went remarkably <*n of 

 well ; and we understand that there we in Wales some buckets. 

 wheels of nearly double this diameter. In circum- 

 stances like this, the double overshot wheel, with a 

 chain of buckets, is a most invaluable machine, not 

 merely from the small price at which it can be erected, 

 but from the great power which it possesses. A ma- 

 chine of this Kind seems to have been first erected by 

 M. Francini in 16C8, in the garden of the king of 

 France's old library. This machine of Francini's was 

 driven by waste water, and raised water from a natu- 

 ral spring, by means of another chain of buckets fixed 

 upon the same wheel. 



M. Coetar substituted a similar machine in place of 

 the overshot wheel ; and more recently Mr Gladstones, 

 an ingenious millwright at Castle Douglas, without 

 knowing that he had been anticipated in the invention, 

 erected several in Galloway for the purpose of giving 

 motion to threshing mills. 



The double overshot wheel is represented in Plate PLATF 

 CCCXX. Fig. 6, where A and B are two rag wheels, CCCXX. 

 as they are called, and CDEF a series of buckets fixed ** s ' 

 to an endless chain, whose links fall into notches in the 

 circumference of the rag wheels. The water issuing 

 from the mill course at MX, is introduced into the 

 buckets on the side C. The descent of the loaded 

 buckets on the side C puts the wheels A and B in mo- 

 tion, and the power is conveyed from the shaft of the 

 wheel A to turn any kind of machinery. When the 

 buckets reach F, they allow the water to escape, and. 

 ascending empty on the side E, they again return to 

 the spout MX, to be filled as before. In this machine, 

 the buckets have in every part of their path the same 

 mechanical effect to turn the wheels, and they will not 

 allow the water to escape till they have reached almost 

 the lowest part of the fall 



This species of wheel possess* 1 ! another advantage, 

 which can be obtained from no other, namely, that oy 

 raising the wheel B, and taking out two or three of 

 the buckets, it may be made to work when there is 

 such a quantity of back-water as would otherwise pre- 

 vent it from moving. 



Dr Hobiaon, in his Dissertation on Water Works, 

 published in the second volume of his Sytfem of Me- 

 chanical Philatopku, has described a machine of this 

 kind, in which plugs, or horizontal floatboards, are 

 fixed to a chain. On the side C these plugs pass 

 through a tube, a little greater in diameter than that of 

 the floats, and the water acting by its pressure upon 

 these floats, as it does in the case of a breast wheel, 

 gives motion to the wheels A and B. 



The double overshot wheel is the best and the most 

 economical which can be adopted for a small supply of 

 water falling from a great height ; but it is liable to get 

 out of order, unless the chain which carries the bucket 

 is made with great care and nicety. 



For farther information on overshot wheels, the read- Reference 

 er is referred to BelidorV/frcMrc/ure Hydrautique, vol. w uuioff 

 ii. p. 254. Desagulier's Courte of Experimental Philo- " r 

 tophy, edit 3d, vol. ii. p. 455. Deparcieux, Mem. Acad. 

 Par. 1754, p. 60S, 671. Smcaton On Mill*, p. 33. 

 Albert Euler, Comment. Soc. Go! ting. 175*. Ktestner, 

 Hydrodyimmiqtie. Lambert, Mem. Acad. Brrl. 1755. 

 Borda, Mem. Acad. Par. 1767, p. 286. Bossut, Trail'' 



