Barxes.—On the Influence of the Earth’s Rotation on Rivers. 98 
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 up-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 
— force of the body is increased and there is a tendency to move 
p-hill, towards the equator. If the motion be from east to west, the 
dhai force is diminished, and the body tends towards the pole. 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 "iut of a stream in lat. 45?, whose 
mean velocity is three miles an hour, is —1,. of the width, which in a 
stream a mile wide is only -+ 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 neutralized, 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 being 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 compact 
and difficult to break up than the loose recent deposit of the river, of which 
the low bank consists. Take for instance the lower course of the river 
Ramgitata, 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 fraction, 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 
