Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/420

 on other different concomitant causes, although they ought all to have connexion with the primary; therefore it is convenient that we propound and examine the several accidents that may be the causes of such different effects.

The first of which is, that when ever the water, by means of a notable retardation or acceleration of the motion of the Vessel, its container, shall have acquired a cause of running towards this or that extream, and shall be raised in the one, and abated in the other, it shall not neverthelesse continue, for any time in that state, when once the primary cause is ceased: but by vertue of its own gravity and natural inclination to level and grow, even it shall speedily return backwards of its own accord, and, as being grave and fluid, shall not only move towards Æquilibrium; but being impelled by its own impetus, shall go beyond it, rising in the part, where before it was lowest; nor shall it stay here, but returning backwards anew, with more reiterated reciprocations of its undulations, it shall give us to know, that it will not from a velocity of motion, once conceived, reduce it self, in an instant, to the privation thereof, and to the state of rest, but will successively, by decreasing a little and a little, reduce it self unto the same, just in the same manner as we see a weight hanging at a cord, after it hath been once removed from its state of rest, that is, from its perpendicularity, of its own accord, to return thither and settle it self, but not till such time as it shall have often past to one side, and to the other, with its reciprocall vibrations.

The second accident to be observed is, that the before-declared reciprocations of motion come to be made and repeated with greater or lesser frequency, that is, under shorter or longer times, according to the different lengths of the Vessels containing the waters; so that in the shorter spaces the reciprocations are more frequent, and in the longer more rare: just as in the former example of pendent bodies, the vibrations of those that are hanged to longer cords are seen to be lesse frequent, than those of them that hang at shorter strings.

And here, for a third observation, it is to be noted, that not onely the greater or lesser length of the Vessel is a cause that the water maketh its reciprocations under different times; but the greater or lesser profundity worketh the same effect. And it happeneth, that of waters contained in receptacles of equall length, but of unequal depth, that which shall be the deepest, maketh its undulations under shorter times, and the reciprocations of the shallower waters are lesse frequent.

Fourthly, there are two effects worthy to be noted, and diligently observed, which the water worketh in those its vibra-