Book 9, of the meeting of rivers and of their ebb and flow. The
cause is the same in the sea, where it is caused by the straits of
Gibraltar; and again it is caused by whirlpools.

[3] If two rivers meet together to form a straight line, and then
below two right angles take their course together, the flow and ebb
will happen now in one river and now in the other above their
confluence, and principally if the outlet for their united volume is
no swifter than when they were separate. Here occur 4 instances.

[Footnote: The first two lines of this passage have already been
given as No. 957. In the margin, near line 3 of this passage, the
text given as No. 919 is written.]

On the alterations, caused in the courses of rivers by their
confluence (972-974).