WATER. 



in which the float acts fliould be in the Hill water fome feet 

 above the plank in which the aperture is made, and have a 

 proper box, or cover, which can be locked up, to fecure the 

 whole. The float (hould be a hollow copper ball, or a glafs 

 bottle, becaufe wood or cork floats abforb the water, and fink 

 deeper therein ; and the rod of wood Ihould be well painted. 

 A flill more perfeft water-gauge is obtained by a fmall ma- 

 chine to keep the regifter ; for this purpofe, let an eight-day 

 clock of the ordinary conftruftion be fixed up in a kind 

 of centry-box, or fmall houfe, over the gauge ; this is to be 

 connected by wheel-work, with a cylindrical barrel, which 

 is to be placed in a perpendicular direftion, and made to turn 

 round once in a week by the clock ; a fheet of paper is 

 wrapped round the barrel, and fattened upon it in the fame 

 manner as paper is faftened on a drawing-board. 



The perpendicular ftem of the float mull have a fmall pencil 

 attached to it, with a flight fpring to caufe it to bear againft 

 the paper on the circumference of the cylinder, fo as to mark 

 •jpon it : in this way the pencil marks, at a different part of 

 the length of the cylinder whenever the float rifes or falls, and 

 the cylinder turning regularly on its axis by means of the 

 clock, caufes thefe rifings and fallings to be marked on dif- 

 ferent parts of the ftieet of paper, fo that when it is removed 

 from the cyhnder it will have a curved line traced upon it, 

 which fliews all the increments and decrements of rife and 

 fall, and affords an exaft regifter of the flow of water, 

 v;hich may be reduced to cubic meafure, by our rules already 

 given. 



A different kind of water-gange has been propofed by M. 

 De Baader : two large cafl<s or other veffels are to be fixed 

 fide by fide, in fuch pofition, that the fl;ream of water may 

 be poured into either of them by a fpout or trough. The 

 fpout is fo contrived, as to turn the llream into one or other 

 of the vcflels at pleafure, with the greateft eafe, but the 

 dream cannot run into both at once. In each veffel is a 

 large float which is ccwnefted with a perpendicular fl:em, 

 fo that the ftem rifes or falls with the float, as the veffels 

 fill or empty ; alfo at the bottom of each veffel is a valve, 

 or fluicc, to allow the water to run out from it, and the 

 perpendicular ftem from the float is provided with means to 

 npen this fluicc, whenever the veffel is full of water, and the 

 Boat rifes to the top, or to fliut the fluice whenever the vef- 

 fel is empty ; and the fame aftion turns the ftream of fupply 

 ■"rom the veflcl which is fuD, into that which is empty. In 

 ;his way, the two veffels aft alternately to receive the water, 

 ind meafure it, for while the fpout runs into one veffel its 

 loat rifes until the veffel is quite full ; the float then turns 

 he fpout and ftream into the other veffel, which we fup- 

 lofe to be already empty, and at the fame moment it will 

 jpen the valve in the bottom of the full veffel ; the water 

 hen begins to run out of the full veffel and to fill the other, 

 s-hich becoming full in turn, its float opens the valve in its 

 )Ottom. In this way the machine continues to meafure the 

 rater, and is provided with a fmall counting machine to re- 

 after the number of reciprocations it has made. 



We have now, as far as our limits will allow, given all the 

 loft ufeful and praftical rules for meafuring flowing water ; 

 nd fliall conclude by obferving, that this is one of the moft 

 itricate and difficult fubjefts in hydraulics, and that no en- 

 ineer can be tuUy competent to dircft the execution of large 

 ■orks without ftudyingthe fubjeft much farther than we have 

 een able to enter into it. Many untried cafes, and combina- 

 lons of cafes, will continually arife, which cannot be decided 

 y any previous knowledge. As a refource for fuch occafions, 

 c fliould be well verfed in the theory of the fubjcft, fo as to 

 lodify the rules laid down for fimple cafes, and adapt them 

 i> his particular cafe, as far as theory can aflift him. 



If he only purfucs the rules laid down by others, without 

 any knowledge of theory, and without entering into the 

 realon and ongm of the rules, his experience wiU not be 

 ot much avail, becaufe he will be unable to correft and im- 

 prove the rules by his own obfervations, or if he attempts 

 to do fo, he may completely fpoil them, by making them 

 falfe m many cafes, in order to obtain truth in fome one cafe. 



To attain the knowledge to which we allude, the follow- 

 ing authors may be confulted. 



Julius Frontinus, De Aquseduftibus urbis Roma Com- 

 mentarius ; written about the year loo, in the time of the 

 emperors Nerva and Trajan. This contains all the know- 

 ledge of the ancients on this fubjeft. It is printed in 

 Graevii Thefaurus Antiquitatum Romanorum, vol. iv. 

 1630 and 1780. A new edition was alfo pubhflied. 



Caftelli, a difciple of Galileo, Delia Mefura dell' acque 

 correnti, 1628. 



TorricelU De Motu Gravium Naturaliter Accelerato, 

 1643. In this work we find the origin of the propofition, 

 that the velocities of iff'uing fluids are as the fquare roots of 

 the depths. 



Raphel Fabrettus de Aquis et Aqueduftibus veteris 

 Romas, 1679. 



Marriotte, Traite du Mouvements des eaux, 1686. This 

 work contains a great number of experiments on the motion 

 of fluids, and particularly on jets of fpouting fluids ; but 

 the reafoning is frequently erroneous. 



Guglielmini, La Mefura dell' acque correnti Alfo, 



Delia Natura dell Fuimi, Bologn. 1697. 



Guglielmini de Fluviis et CafteDis Aquarum. Thefe 

 contain a theory which has long fince been exploded. He 

 firft attempted to apply the principles of falhng bodies to 

 the motion of waters in open canals and rivers. 



Polenus, De Motu aqua: Mixto, Patav. 1697, 1718, 1723. 



Parent Mem. Acad. Par. 1700. 



Newton's Principia, 1687. This work contains the doc- 

 trine, that the velocity of a fpouting fluid is equal to that 

 which a heavy body .acquires in falling through half the depth 

 of the column ; but which is not correft. And in the fecond 

 edition, 1713, Newton firft points out the contrafted vein, 

 and the proportion of its area to that of the orifice to be, as 

 .707 to I. 



Polenus De Caftellis per qusE derivantur fluviorum aqua:, 

 Padua, 1 7 1 8. He ftates the area of the contrafted vein to be 

 .571 of the area of the orifice, and he difcovered, that more 

 water is yielded by a cyhndrical pipe than by a fimple 

 orifice. 



Michelotti, De Separatione Fluidorum in Corpore Ani- 

 male, 1719. 



Dr. Jurin, " On the Motion of running Water," pub- 

 lifned in the Philofophical Tranfaftions for 1718 and 1722. 

 Lowthorp's Abridgment, vol. vi. p. 341. 



Raccolta De Autori die Trattano dell Moto dell' acque, 

 3 torn. 4to. Florence, 1723. This moft valuable collec- 

 tion contains the writings of Archimedes, Albizi, Galileo, 

 Caftelli, Michclini, Borelli,Montanari, Viviani, Caflini, Gug- 

 lielmini, Grandi, Manfredi, Picard, and Narducci ; and an 

 account of the numberlefs works which have been carried 

 on, in the imbankment of the river Po in Italy. 



M. Couplet, Des Recherches fur le Mouvement des eaux 

 dans les tuyaux de conduit. Memoires de I'Acad. 1732. 

 This is on the motion of water in pipes, and is given by 

 Belidor in his Arch. Hydraulique. 



Architefture Hydraulique ou I'Art de Conduire d'elever 

 et de menager les eaux pour les differens befoins de la vie, 

 in 4 vols. 4to. par M. Belidor, Commiffaire Provincial 

 d'Artilleric, Paris, 1739. 



Daniel 



