Blowing Machine. — Drainage •without Engines 491 



the water, the quantity of the mixture of the water and air which pafles in a fecond 

 through K L is=6, i a^V {a+b — 1,4). We niuft deduft from the quantity {a+b — 1,4) 

 that height which anfwers to the velocity the water muft lofe by that portion of ve- 

 locity which it communicates to the air laterally introduced ; but this quantity is fo fmall 

 that it may be neglefted in the calculation. The water which pafles in the fame time of 

 one fecond through B C is = 0,4 a^ V (a + 0,1). Confequcntly, the quantity of air 

 which pafles , in one fecond through K L, will be=6, i a"- V {a-\-l> — 1,4) — 0,4 a^V 

 (a +0,1), taking the air itfelf, even in its ordinary ftate of compreflion, under the weight 

 of the atmofphere. It will be proper, in praftical applications, to dedudt one-fourth from 

 this quantity; I, on account of the Ihocks which the fcattered water fuftains againft the in-- 

 ferior part of the tube, which deprive it of part of its motion ; and, 2, becaufe it muft happen 

 tliat the air in L K will not, in all its parts, have acquired the fame velocity as the water. 



If the pipe O'do not difcharge the whole quantity of air afltirded by tlie fall, tlie water 

 will defcend at X Z; the point K will rife in the pipe, the afflux of air will' diminijh, and 

 part of the wind will iflue out of the lower lateral apertures of the pipe B K. 



r (hall not here examine the greater or lefs degree of perfeftion of the difi"erent forms of 

 water-blowing machines, which are ufed at various iron forges, fuch as thofe of the Catalans, 

 and elfewhere. Thefe points may. be eafily determined from the principles here laid down; 



PROPOSITION IX.. 



It is pojthle, by means of a fall of ivater, to drain a piece of ground., nvithotft the help of machines ; ■ 

 even though the ground fhould lie on a lower level, than the ejlabltfhed current, below the fall. 



The means of doing this is pointed out in the firft experiment of this treatife. We have 

 feen that the water contained in the veflel D E F B, fig. 3. Plate VIII. ifllies through the 

 channel M B V, which is higher than the furface of the water itfelf, becaufe the fluid which 

 pafles through A C carries with it the water contained in the veifel. 



In the artificial fall, which is procured' in channels to give motion to mills, when the 

 water ruflies down by a re£fcangular trunk of wood, D B C F, fig. 1 7, placed nearly horizon- 

 tal in the middle of the lower channel, the furface of the water at K is one or two feet 

 Beneath the inferior current (or back-water) F L*. The water at F tends to return and defcend 

 along F K ; but the current, by its lateral adlion, confliantly carries it away, and does not permit 

 it to Aide down to K. If an opening G be made in the lateral fides of the trunk, the waters from 

 lands lower than the current of the inferior ftream F L may be drained oS. In a commiflion 

 with feveral'of my colleagues, I once propofed, that tliis principle fliould be applied to a cafe 

 of pradlice. The projcft was adopted, and the drainage fucceeded very welL 



The reflangular conduit D D F C muft be prolonged to a certain extent along the lower 

 channel, otherwife the water might flow back from F to K, and oppofe the drainage through G. 

 The mill-wrights are aware of the utility of this prolongation. Experiment has taught 



* This depreflion of the level has already been noticed in K. Guilielmi, della natura de fiumi, cap. 7, 

 fig. 46. Boflut, art. 7:1, The whe«l alluded to in the text muft, I preiumt, be of that kind which we 

 call a breaft- wheel. — N. 



tlieni= 



