Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/416

 I have all the while perfectly apprehended you in this; and I stand greedily attending to hear in what manner these wonders may occur without obstruction from the motion already assigned to the Earth.

These effects being to ensue in consequence of the motions that naturally agree with the Earth, it is necessary that they not onely meet with no impediment or obstacle, but that they do follow easily, & not onely that they follow with facility, but with necessity, so as that it is impossible that it should succeed otherwise, for such is the property & condition of things natural & true. Having therefore shewen the impossibility of rendring a reason of the motions discerned in the Waters, & at the same time to maintain the immobility of the vessel that containeth them we may proceed to enquire, whether the mobility of the Container may produce the required effect, in the manner that it is observed to evene.

Two kinds of motions may be conferred upon a Vessel, whereby the Water therein contained, may acquire a faculty of fluctuating in it, one while towards one side, and another while towards another; and there one while to ebbe, and another while to flow. The first is, when first one, and then another of those sides is declined, for then the Water running towards the inclining side, will alternately be higher and lower, sometimes on one side, and sometimes on another. But because that this rising and abating is no other than a recession and accession to the centre of the Earth, such a motion cannot be ascribed to the Cavities of the said Earth, that are the Vessels which contain the Waters; the parts of which Vessel cannot by any whatsoever motion assigned to the Earth, be made to approach or recede from the centre of the same: The other sort of motion is, when the Vessel moveth (without inclining in the least) with a progressive motion, not uniform, but that changeth velocity, by sometimes accellerating, and other times retarding: from which disparity it would follow, that the Water contained in the Vessel its true, but not fixed fast to it, as its other solid parts, but by reason of its fluidity, as if it were separated and at liberty, and not obliged to follow all the mutations of its Container, in the retardation of the Vessel, it keeping part of the impetus before conceived, would run towards the the preceding part, whereupon it would of necessity come to rise; and on the contrary, if new velocity should be added to the Vessel, with retaining parts of its tardity, staying somewhat behind, before it could habituate it self to the new impetus, it would hang back towards the following part, where it would come to rise something. The which effects we may plainly declare and make out to the Sense by the example of one of those same Barks yonder, which continually come from