Baines. — On the Influence of ike Earth's Flotation on JRivers. 93 



centrifugal force ceased, the body would evidently move towards the nearest 

 pole, as down a hill. From the poles to the equator may therefore be 

 regarded as u]3-hill — bodies free to move being prevented from going down 

 towards the poles by centrifugal force. Suppose, now, a body to move from 

 west to east, that is, in the same direction as the earth revolves ; the 

 centrifugal force of the body is increased and there is a tendency to move 

 up-hill, towards the equator. If the motion be from east to west, the 

 centrifugal force is diminished, and the body tends towards the x^ole. In 

 each case the tendency is towards the right in the northern hemisphere and 

 towards the left in the southern. 



The deflecting force arising from the earth's rotation being a horizontal 

 force acting always at right angles to the direction of motion, its effect on a 

 stream in the southern hemisphere must be to raise the water-level at the 

 left bank and lower it at the right, and this difference of level by increasing 

 the depth would increase the velocity, and consequently the erosive power at 

 the left bank. It might appear that the wearing away of the left banks of 

 rivers in the southern hemisphere is thus accounted for, but examination 

 will make it evident that this explanation is insufficient. It will be shown 

 that the difference of level at the opposite sides of a stream in lat. 46°, whose 

 mean velocity is three miles an hour, is ^^l^^ of the width, which in a 

 stream a mile wide is only -5- inch. The effect of the small difference in 

 the erosive power, due to that difference of level — in causing unequal 

 wearing away of the banks — would be neutrahzed, if the left bank were 

 composed of slightly harder material than the right ; or if the left bank were 

 a little higher, so that the quantity of material to be removed for each foot 

 cut away horizontally would be greater than at the right. The small 

 difference of erosive power could not explain how it is that, as a general 

 rule, the bank which is bemg worn away is much the highest, the opposite 

 bank being, in many rivers, below flood level, especially when it is taken 

 into consideration that the material below the water-line at the high bank 

 has been consolidated by superincumbent pressure, and made more comjoact 

 and difficult to break up than the loose recent deposit of the river, of which 

 the low bank consists. Take for instance the lower com-se of the river 

 Eangitata, where there is a high terrace on the left, and a low plain on the 

 right. The erosive power at the left bank would have to be many times, 

 instead of a small fi-action, greater than at the right, to account for the high 

 terrace being cut away instead of the low plain. 



I shall try to show that the changes in river-courses are due to the 

 unequal velocities of the surface and bottom layers of running water. 



In ordinary streams the velocity increases nearly uniformly from the 

 bottom to the surface, the deflecting force being proportional to the 



