jjpa C^nfiderattons refpeciing Eddies in Water, 



them, that it prevents the water from retumiflg back fo readily in the time of floods, which 

 might check the motion of the water-wheel. For this purpofe, they make the upper part D F 

 at the height of the waters, which the mill-ftream can refift or fupport. The town of Final, 

 in the territory of Modena, having charged me with the dire£lion of changing the courfe of 

 part of the waters of the Panaro, which the circumftances of the town required to be donej 

 i availed myfelf of this prolongation of the tail-pipe D F, combined with other artifices, to 

 ifnaintain the aftion of mills in the new channel; and I fucceeded not only beyond the expec- 

 tation of the inhabitants, but even beyond my own hopes. 



PROPOSITION X. 



The eddies of the water in rivers are produced by motion, communicated from the more rapid parts 

 of thefiream to the lateral parts, -which are more at reft. 



■ Few authors have examined the caufc and the efFe£l:s of the eddies of water in rivers ; and 

 thofe who have undertaken this inveftigation, do not appear to have been very happy in their 

 refearches. 



The water which moves in the channel M N H, fig. 19. meets the obftacle B A, which 

 impedes its courfe, and caufes it to rife and difcharge itfelf in the diredlion A C with an in- 

 creafed velocity. Suppofe the water in B D C A to be dormant, the current A C communis 

 cates its motion to the lateral particles E (Prop. I.), and conveys them forward ; the furface of 

 the dormant water becomes deprefled at E, and the mod remote particles towards D are urged 

 according to the laws of the equilibrium of fluids to fill the depreflion. The current A C 

 continues to carry them off, and the fpace B D C A continues to be exhaufted. The water 

 . of the current A C, by virtue of the fame laws, is a£led upon by a conftant force which urges 

 it towards the cavity E, while its natural courfe or projedlion carries it towards A C. Under 

 the agency of thefe two forces, the water A C acquires a curve-lined motion in C D, and de- 

 fcends as it were through an inclined plane, becoming retrograde in D E, whence it would 

 proceed to ftrike the obftacle B A, and the current A C, after which, it would undergo feveral 

 ofcillations previous to acquiring a ftate of equilibrium and repofe. But the current A C 

 continues its lateral a£lion : a fecond time it draws away the water through C D into E, and 

 forces it to renew its motion through the curve C D E; in which manner the eddy continues 

 without ceafing. 



If the river fhould pafs through a contraftion of its bed at N, it will produce eddies on both 

 fides, atP and at Q, fimilar to thofe we have contemplated at D C. 



Suppofe the ftream of water, after having ftruck the bank G H, to be reflected into a new 

 diredtion H S, tlie lateral communication, of motion will excite eddies in the angle of reflec- 

 tion R. 



When two currents of unequal velocity meet obliquely in the middle of the river, the moft 

 rapid current will produce eddies in that which is the leaft rapid. 



Suppofe a ftream of water to flow over a bed of unequal depth. If the longitudinal fcflion 

 of the inequalities of the bottom exhibit a gentle flope, as at A B C, fig. 20. the fuperior 

 water will imprcfs its motion by lateral communication upop^he inferior water, which is near 

 the bottom, beneath the line A C, and a current will take place through the whole depth of 



the 



