EBB AM) FLOW. 193 



trade winds, which return at regular periods of the year. 

 That in consequence of these and similar causes, they 

 vary their states of flow and eddy, both as relates to 

 extending and widening the motion itself, and to the velo 

 city and measure of the motion ; and thus produce what 

 we term currents. Thus in the seas the depth of the basin 

 or channel, the occurrence of whirlpools or submarine 

 rocks, the curvature of the shore, gulfs, bays, the various 

 position of islands, and the like, have great effect, acting 

 powerfully on the waters, their paths, and agitations in all 

 possible directions, eastward and westward, and in like 

 manner northward and southward ; wherever, in fact, such 

 obstacles, open spaces, and declivities exist in their res 

 pective formations. Let us then set aside this particu 

 lar, and, so to speak, casual motion of the waters, lest 

 it should introduce confusion in the inquisition which we 

 now pursue. For no one can raise and support a denial 

 of the statement which we are presently to make, concern 

 ing the natural and catholic motions of the seas, by 

 opposing to it this motion of the currents, as not at all 

 consistent with our positions. For the^ currents are mere 

 compressions of the water, or extrications of it from com 

 pression : and are, as we have said, partial, and relative to 

 the local form of the land or water, or the action of the 

 winds. And what we have said is the more necessary to 

 be recollected and carefully noted, because that universal 

 movement of the ocean of which we now treat is so gentle 

 and slight, as to be entirely overcome by the impulse of 

 the currents, to fall into their order, and to give way, be 

 agitated, and mastered by their violence. That this is 

 the case is manifest particularly from this fact, that the 

 motion of ebb and flow, simply, is not perceptible in mid 

 sea, especially in seas broad and vast, but only at the 

 shores. It is therefore not at all surprising that, as inferior 

 in force, it disappears, and is as it were annihilated amidst 

 the currents; except that where the currents are favourable, 

 it lends them some aid and impetuosity, and on the con 

 trary where they are adverse considerably restrains them. 

 Waiving then the motion of the currents, we proceed to the 

 four regular motions; that in the six hours, in the month, 

 in the half month, and in six months, of which the sex- 

 horary motion alone seems to produce and develope the 

 ordinary tide, the monthly to determine that motion and 

 define its renewal ; the half monthly and half yearly to in 

 crease and strengthen it. For the ebb and flow which cover 

 VOL. xv. o 



