Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/417

 * Lizza-Fusina, laden with fresh water, for the service of the City. Let us therefore fancy one of those Barks, to come from thence with moderate velocity along the Lake, carrying the water gently, of which it is full: and then either by running a ground, or by some other impediment that it shall meet with, let it be notably retarded. The water therein contained shall not, by that means, lose, as the Bark doth, its pre-conceived impetus, but retaining the same, shall run forwards towards the prow, where it shall rise notably, falling as much a stern. But if, on the contrary, the said Bark, in the midst of its smooth course, shall have a new velocity, with notable augmentation added to it, the water contained before it can habituate it self thereto, continuing in its tardity, shall stay behinde, namely a stern, where of consequence it shall mount, and abate for the same at the prow. This effect is undoubted and manifest, and may hourly be experimented; in which I desire that for the present three particulars may be noted. The first is, that to make the water to rise on one side of the vessel, there is no need of new water, nor that it run thither, forsaking the other side. The second is, that the water in the middle doth not rise or fall notably, unlesse the course of the Bark were not before that very swift, and the shock or other arrest that held it exceeding strong and sudden, in which case its possible, that not only all the water might run forwards, but that the greater part thereof might issue forth of the Bark: and the same also would ensue, whilst that being under sail in a smooth course, a most violent impetus should, upon an instant, overtake it: But when to its calme motion there is added a moderate retardation or incitation, the middle parts (as I said) unobservedly rise and fall: and the other parts, according as they are neerer to the middle, rise the lesse; and the more remote, more. The third is, that whereas the parts about the midst do make little alteration in rising and falling, in respect of the waters of the sides; on the contrary, they run forwards and backwards very much, in comparison of the extreams. Now, my Masters, that which the Bark doth, in respect of the water by it contained, and that which the water contained doth, in respect of the Bark its container, is the self-same, to an hair, with that which the Mediterranean Vessel doth, in respect of the waters in it contained, and that which the waters contained do, in respect of the Mediterranean Vessel their container. It followeth now that we demonstrate how, and in what manner it is true, that the Mediterrane, and all the other Straits; and in a word, all the parts of the Earth do all move, with a motion notably uneven, though no motion that is not regular and uniforme, is thereby assigned to all the said Globe taken collectively.