CHAP. I. OF THE EBB AND FLOW OF THE SEA.

the reasons that could support the opinion that the moon was the primary cause of the ebb and flow. However, as in matters of physics one can never be too certain of the facts, M. Cassini Jacques Cassini (1677–1756), also known as Cassini II, a French astronomer who conducted extensive research on the shape of the Earth and the movement of tides. continued to provide in 1712, 1713, 1714, and 1720 a series of other memoirs, always based on new and very precise observations made at Brest, Bayonne, and the port of L’Orient, which confirm the conclusions he had drawn from the first ones. These leave today less doubt than ever that it is to the combined action of the moon and the sun that we must attribute the ebb and flow of the sea.

It is by making use of these memoirs, and the judicious remarks communicated to us by Messrs. Bouguer Pierre Bouguer (1698–1758), a French mathematician and "the father of naval architecture," known for his work on hydrography. and de Caux, that we have put ourselves in a position to write this chapter. Here, we have also mentioned the most reasonable things said by Cesar d’Arcons regarding the effects of tides in his treatise on the ebb and flow of the sea, without regard for the sentiment of that author on the cause he attributes to a regular balancing of the earth on its axis, from south to north and north to south, twice in 24 hours. We set this aside because the philosophers of his time were more occupied with creating hypotheses than with studying and closely following the conduct of nature. For the rest, we exhort those who wish to be even better informed of the knowledge for which we are indebted to M. Cassini to read what he has written in the Memoirs of the Academy for the years we have just cited, as we have reported what follows only as it relates to our objective.

Definition of the ebb and flow of the sea, and in what order they occur each day.

583. Few people are unaware that the sea, coming from the torrid zone The region of the Earth between the Tropics of Cancer and Capricorn; the tropics. and moving toward the poles, rises twice each day on the coasts of the Ocean; that it takes a little more than six hours to reach its greatest height, where it remains for a few minutes in the same state, which is what is called high tide; then it retreats by descending for a little more than six other hours until its lowest point, where it again remains stationary for some time; after which it rises as before. It is these alternatives that are called ebb and flow. It should be observed that the flow or the flood refers to its movement when it is rising and has not yet reached its greatest height, and that the ebb, the ebbe, or the joussant original: "le reflux, l'ebe, ou le joussant"; historical maritime terms for the falling tide. refers to its action when it descends while approaching its lowest limit, which constitutes low tide.

As each of these movements lasts a little more than six hours, there are also a little more than 12 hours between two full