484 FOURTH REPORT 1834. 



fluenced by extenial causes ; — that the inequalities of the soil, to- 

 gether with artificial obstacles which rivers encounter in their 

 courses, are the causes of the bends, sinuosities, and irregulari- 

 ties which constantly exist in them ; — that rivers which carry 

 gravel preserve their direction with great difficidty, on account 

 of the alterations which continually take place in the time of 

 floods by partial depositions ; — that in consequence it is exceed- 

 ingly difficult to regulate such rivers by artificial works, but 

 much less so where rivers run through sand or other homoge- 

 neous beds. 



Chapter the 8th contains several interesting observations re- 

 lative to the junctions of rivers with each other and with the sea. 

 In times of flood the elevation of the water is less sensible at 

 the embouchures than above them, but a few inches of elevation 

 at the embouchure occasions an elevation of several feet in the 

 river. The velocity also, although stated by Guglielmini to be 

 greater, is actually less at the embouchure than above it. 



The author finishes this chapter by examining the cases of 

 rivers joining each other perpendicularly or obliquely, and when 

 they are subject to the flux and reflux of tides, and consequent 

 changes in the directions of the embouchures. 



Chapter the 9th treats of the effects resulting from the union 

 of rivers with each other, and with the sea. In the 1st propo- 

 sition it is stated that if two rivers similar in section and volume 

 empty themselves separately into the sea, the sum of their sec- 

 tions will be greater than if they entered the sea in one united 

 bed. The author adduces the sections made of the Reno and 

 Tecino, affluents of the Po, in the year 1719 as proofs of this 

 assertion. In proposition the 2nd he states. That two rivers 

 united in one bed have greater velocity and power of corrosion 

 of the bed than two rivers running in separate beds, and the 

 increased eff"ect will not only take place below, but above the 

 confluence of the two rivers ;— that the breadth and section will 

 be less in the united than the disunited rivers ; — lastly, respect- 

 ing the effects of tides in keeping open the mouths of rivers, that 

 the water of the sea, which during the flood enters into the beds 

 of rivers, returning back with the ebb, helps to clean out the bed 

 and to sweep away the deposits. He has repeated this doctrine 

 elsewhere, expressing his opinion that so long as rivers could of 

 themselves keep their mouths open on a flat shore, the agitation 

 of the tides would prevent any shoals fi'om forming in the trunk 

 lying above the mouth ; and with regard to the entrance of rivers 

 into the sea, that the form of the mouth will depend upon the 

 difference of velocity between the river and tide currents : that the 

 sediments of the river will settle along the eddy part of the shore 



