446 



Experiments 011 Velocity of Water. 



slope. The Scotch Lochs have been attributed in 1862 to erosion, or excava- 

 tion by glacial action, by Mr. J. F. Jamieson, the eminent Scotch geologist, 

 who observed that boulders had been pushed by ice uphill 700 feet (Quart. Jour. 

 Geol. Soc, vol. xviii., page 178). Professor Karnsay, page 203 op. cit., takes 

 the same view of the glacial origin of the Scotch Lochs. 



An approach to uniform motion occurs in all rivers except when there are 

 floods. 



Fig. 5 represents the slope of the surface of a large river, corresponding 

 closely with the theoretical curve, a parabola of the form drawn. 



Fig. 5A gives the deviation from the true curve, in feet, at 22 towns. 



The bed of the river acquires such a cross section that water may flow in 

 uniform motion from one end of the river without the back water overtaking 

 the front water in the river. Fig. 5B represents a transverse section of a valley. 



(12) Diagrams Figs. 6 and 7 represent a stream of water in an artificial channel, 



LOUCHE 



VARIABLE HOfCoH 



at one point in variable motion, and at the other in uniform motion. I is the 

 slope per metre. 



In the experiments, the water ran about forty yards before it obtained uni- 

 form motion. 



The depth of the stream represents what may be termed the stand up, or 

 stability of the stream for that particular quantity flowing, and the particular 

 slope and material of channel. A and a represent cross sections ; V and v, 

 velocities ; O and q discharges ; I and i slopes of the different channels 

 compared. The velocity increases as the cube root of the increase of quantity 

 at the same slope, ane the velocity increases as the cube of the increased slope 

 when the quantity flowing is the same. 



(13) Fig. 8 shows the different effect of depth and velocity for a certain small 

 quantity flowing at the same slope as a larger quantity. The velocity in D 

 channel when twelve times the quantity is flowing of that in B, is 2 '3 times that 

 in B. That is, the change is from 0*502 to 1*278, and 23 is the cube root of 

 12-167. 



