Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/424

 flowing is wholly annihilated, or at least very much obscured. I passe by the continual alteration of the air, which disquieting the water, permits us not to come to a certainty, whether any, though but small, encrease or abatement of half an inch, or losse, do reside in the Straights, or receptacles of water not above a degree or two in length.

I come in the second place to resolve the question, why, there not residing any vertue in the primary principle of commoving the waters, save onely every twelve hours, that is to say, once by the greatest velocity, and once by the greatest tardity of motion; the ebbings and flowings should yet neverthelesse appear to be every six hours. To which is answered, that this determination cannot any wayes be taken from the primary cause onely; but there is a necessity of introducing the secondary causes, as namely the greater or lesse length of the Vessels, and the greater or lesse depth of the waters in them conteined. Which causes although they have not any operation in the motions of the waters, those operations belonging to the sole primary cause, without which no ebbing or flowing would happen, yet neverthelesse they have a principal share in determining the times or periods of the reciprocations, and herein their influence is so powerful, that the primary cause must of force give way unto them. The period of six hours therefore is no more proper or natural than those of other intervals of times, though indeed its the most observed, as agreeing with our Mediterrane, which was the onely Sea that for many Ages was navigated: though neither is that period observed in all its parts; for that in some more angust places, such as are the Hellespont, and the Ægean Sea, the periods are much shorter, and also very divers amongst themselves; for which diversities, and their causes incomprehensible to Aristotle, some say, that after he had a long time observed it upon some cliffes of Negropont, being brought to desperation, he threw himself into the adjoyning Euripus, and voluntarily drowned himself.

In the third place we have the reason ready at hand, whence it commeth to passe, that some Seas, although very long, as is the Red Sea, are almost altogether exempt from Tides, which happeneth because their length extendeth not from East to West, but rather transversly from the Southeast to the Northwest; but the motions of the Earth going from West to East; the impulses of the water, by that means, alwayes happen to fall in the Meridians, and do not move from parallel to parallel; insomuch that in the Seas that extend themselves athwart towards the Poles, and that the contrary way are narrow, there is