REPORT ON HYDRAULICS. — PART II. 473 



river is generally y'^th greater than the mean velocity t; s= 1 '494 met. 

 As the current, however, was prevented from entering the arches 

 by fenders, placed to protect the piers from the ice, it was neces- 

 sary to adopt Eytelwein's coefficient of contraction, or 0"855 ; 

 L, or breadth of the river, being 180" 7 metres, and h, or depth 

 of the river, being 53*7 ; from which we get the numerical value 



f .... - ^ (l-494)n 180- 7 X 5-3 7 , , n 



of ^,whichis equal ^o ^^^ ^,^^^ ^ ^^ ^^.^^ ^ ^^ - l.| 



TVT 1 .• 5-37 



Neglectmg ^:3^-^, 



we have the first value oi x = 0*437 metres. 



second . . ditto = 0'358 — 



third . . . ditto =0-370 — 



fourth and last, being the result of calculation, = 0*369 — 



whilst that of the experiment is = 0'383 — 



but such results must necessarily depend upon circumstances. 



Progress of Hydraulic Engineering in England tvith reference 

 to Rivers, Canals, and Drainage. 



Though practical works in hydraulic engineering of great mag- 

 nitude and extent have been carried on in England, the applica- 

 tion of this science to rivers has made little or no progress here 

 since its first introduction from the Continent. The demands of 

 of commerce have made us partially acquainted with some of the 

 common phaenomena which they present ; but the laws which 

 govern their motions, under all the variable circumstances to 

 which they are subject, are involved m mystery. The principles 

 upon which the earliest Acts of Parliament were framed for the 

 conservancy of our rivers consisted in deepening, straightening, 

 and embanking them where necessary, and, by means of sluices 

 and weirs, penning up or lowering the surface of the water for 

 the purpose of producing flashes and overcoming the obstruc- 

 tions to navigation. Experience had, however, shown that na- 

 vigations of this sort were liable to perpetual degradation, from 

 the alterations produced in the regimen of the rivers by such 

 artificial works, which frequently augmented instead of remedy- 

 ing the evil, whilst they obstructed the general drainage of the 

 country. 



The circuitous navigation and the trackage against the stream 

 were at all times laborious and dilatory; these difficulties sug- 

 gested the propriety of deserting the natural bed of the river, 

 and led to the formation of separate cuts mth the pound locks*, 



* The first lock in England is supposed to have been erected in the year 1675, 

 on the Exeter navigation. 



