496 BACK-WATERS. 



experiments that the back-water created by the influence 

 of the tides will extend up a river, for a considerable 

 distance beyond the actual limits of their high water 

 level: the water assuming, as we have said, more or 

 less the condition of an inclined plain; a series of 

 recent observations made by the French engineers 

 on the river Rhone, seem to have placed this 

 fact almost beyond question. The proverb that 

 "water will always find its own level," must there- 

 fore be received with reservations, as only true in 

 part. Strictly speaking for instance, the cross section 

 of river currents probably always assume more or less 

 the form of a curve, convex in the centre; and in 

 rapids this uprising of the water in midstream is some- 

 times quite visible to the eye. Then as regards the 

 ocean (our nearest approach to a true plane surface) 

 this also as we know, visibly follows the arc of the 

 earth's circumference (this is something about i in 2437), 

 and in fact, actually does form a liquid circle engirdling 

 the globe. The familiar figure of ships seen at sea, 

 hull down below the horizon, is of course the result 

 of this curvature, which amounts to about 2 feet 2 

 inches in the mile: an object the height of a man is 

 thus hidden from the eye, at sea-level, at a distance 

 of about 2-J miles. 



The immense rise of the Gangetic floods, which over- 

 spread a vast area of land, not only alters largely the 

 level of the water, but also removes those natural 

 impediments to the current above alluded to ; therefore, 

 as the level of the Bay of Bengal remains constant, 

 the seaward end of its course becomes transformed 

 into rapids of a highly dangerous character. 



Thus the Hooghly, one of its principal branches, 



