Hydraulic Architecture, Volume 2, Part 2

HYDRAULIC ARCHITECTURE, BOOK III.

We see, therefore, the reason why, when examining the sea along coasts situated to the east, it appears to move everywhere from east to west and from west to east, because one does not perceive what is happening several leagues A league is a historical unit of distance, typically measuring about 3 miles or 4.8 kilometers. out at sea; and when one is positioned on shores facing south, one is inclined to believe that it moves from north to south and from south to north. One should no longer be surprised, then, if it is observed almost everywhere that the waters of the sea carry themselves directly toward the coasts during the flow The rising of the tide. and take a contrary route during the ebb The falling of the tide..

Examination of what occurs in the Mediterranean Sea regarding the flow and ebb.

599. The common opinion is that the Mediterranean Sea has no regulated tide, and that the little flow found there is caused by the winds, except along the southernmost coasts of Spain, where it participates greatly in the flow and ebb of the Ocean through the Strait of Gibraltar; but when one examines this sea at more distant shores, such as along those of Italy, one sees that it rises or falls by about one foot, and much more so at Venice, where the tides rise up to 3 feet. This is because there, its north-south extent is greater than elsewhere by the entire length of the Adriatic Gulf, in which the waters, being pushed by the general cause of the tides, press against one another until the end of the gulf; since the gulf narrows continuously, the sea swells because it cannot expand in width. This would not happen if the action of the flow and ebb did not take place upon this sea. One can be all the less mistaken about this because it only occurs at the time of the syzygies The periods of the New Moon and Full Moon, when the Sun, Earth, and Moon are aligned, creating the strongest gravitational pull and highest tides., while during quadratures The periods when the Moon is at a right angle to the Sun relative to the Earth, resulting in the smallest tidal range. it almost neither rises nor falls at Venice, where the flow is usually most marked. For one must not confuse its natural increases with the elevation to which it sometimes rises when swollen by southerly winds that drive it toward the coasts of Europe.

The regular movement of the waters in the Strait of Messina and in that of Chalcedon is proof that the Mediterranean Sea has a flow and ebb.

600. A convincing proof that this sea flows and ebbs is that each time the waters begin to increase on the coasts of Italy due to the arrival of the tide, they enter the Strait of Messina from both ends at the same time, ebbing there for 6 hours against one another until the middle, where they collide and intermingle; after which they flow and exit also by both ends during the following 6 hours. This comes from the layout of this strait, which is 12 great leagues long, and which separates, as one