4S 2 



Causes of Shape of Symmetrical Hills. 



all are at the same slope : this is owing to the effect that quantity flowing has upon 

 velocity. Thus the velocity in F is 2-047 5 m H, 1 "628 ; and in G and K, 1 -274. 



(21) The channels in Fig. 18 are taken from four observed cases of water in 

 uniform motion ; and if a channel was divided, as shown in Fig. 18, the above 

 would be the real velocity. 



These new laws, already spoken of, might be applied in practice to such a 

 river as the Nile to produce longer irrigation. 



Fig. 18. The mean velocity would be much reduced by dividing the river much 

 higher than the present Delta. If three or more artificial channels were made, 

 the streams would be much deeper and slower, although at the same slope as 



FIG. IS 



MfJUNLT TABMl^^**'*^ FR0M A £H0TO 



at present ; and they would, and might, give an irrigation to the desert of Egypt, 

 which would be of immense agricultural value, by causing an earlier and larger 

 overflow of the Nile. The opposite is also true, that rivers joined at the same 

 slope traverse with greater velocity. If the rivers of the Rhine Delta were 

 joined so as to have one mouth, the Rhine would have a deep navigable mouth, 

 and the stream, by its velocity, would always keep 22 feet of water at the bar. 



Fig. 20 is a diagram, the outline of which is a true binomial curve. This curve 

 is shown in dotted line on Fig. 19, Mount Tabor, a type of a certain class of hills.* 



Another common form is also shown in Fig. 21 ; the hills assume the fish- 

 back outline, the water-shed dividing the hill into unequal parts. 



FIG.20 



BINOMIAL tURVEIDRRtJH 

 FtiOM THE COEFFICIENTS 



op a*b>°\ AS ORDINATE 



i T j 



J 10 45 ISO 810 552 ElO ISO 45 10 1 



The letters W W indicate the water-sheds. Fig. 2IA and 2IB are the binomial 

 curves set out in a proper manner from the coefficients of (a + b) 10 . The water- 

 shed being out of the centre in Fig. 21 produces a different form to Fig. 19. 



Fig. 29, p. 460, Black Gang Chine, represents the effect of erosion and denu- 



x " The best general definition of a hill is that it is the convex portion of ground (B A B) 

 lying above the concave part, or valley (B VI). The springs burst out most at B and B, and 

 make that part of the curve the steepest (see Fig. 20). Although the surface of Fig. 19 appears 

 smooth, it is no doubt a succession of small walls and slopes. 



