WHY THE SEA MAKES A STRONGER CURRENT IN THE STRAITS OF SPAIN THAN
ELSEWHERE.

A river of equal depth runs with greater speed in a narrow space
than in a wide one, in proportion to the difference between the
wider and the narrower one.

This proposition is clearly proved by reason confirmed by
experiment. Supposing that through a channel one mile wide there
flows one mile in length of water; where the river is five miles
wide each of the 5 square miles will require 1/5 of itself to be
equal to the square mile of water required in the sea, and where the
river is 3 miles wide each of these square miles will require the
third of its volume to make up the amount of the square mile of the
narrow part; as is demonstrated in _f g h_ at the mile marked _n_.

[Footnote: In the place marked A in the diagram _Mare Mediterano_
(Mediterranean Sea) is written in the original. And at B, _stretto
di Spugna_ (straits of Spain, _i.e._ Gibraltar). Compare No. 960.]