Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/419

 there are such contrarieties of motions in the parts of the Terrestrial Surface, whilst it turneth round upon its own centre, it is necessary, that in conjoyning this Diurnal Motion, with the other Annual, there do result an absolute motion for the parts of the said Terrestrial Superficies, one while very accelerate, and another while as slow again. The which is manifest, considering first the parts about D, the absolute motion of which shall be extream swift, as that which proceedeth from two motions made both one way, namely, towards the left hand; the first of which is part of the Annual Motion, common to all the parts of the Globe, the other is that of the said point D., carried likewise to the left, by the Diurnal Revolution; so that, in this case, the Diurnal motion increaseth and accelerateth the Annual. The contrary to which happeneth in the opposite part F, which, whilst it is by the common annual motion carried, together with the whole Globe, towards the left, it happeneth to be carried by the Diurnal conversion also towards the right: so that the Diurnal motion by that means detracteth from the Annual, whereupon the absolute motion, resulting from the composition of both the other, is much retarded. Again, about the points E and G, the absolute motion becometh in a manner equal to the simple Annual one, in regard that little or nothing increaseth or diminisheth it, as not tending either to the left hand, or to the right, but downwards and upwards. We will conclude therefore, that like as it is true, that the motion of the whole Globe, and of each of its parts, would be equal and uniforme, in case they did move with one single motion, whether it were the meer Annual, or the single Diurnal Revolution, so it is requisite, that mixing those two motions together, there do result thence for the parts of the said Globe irregular motions, one while accelerated, and another while retarded, by means of the additions or substractions of the Diurnal conversion from the annual circulation. So that, if it be true (and most true it is, as experience proves) that the acceleration and retardation of the motion of the Vessel, makes water contained therein to run to and again the long wayes of it, and to rise and fall in its extreames, who will make scruple of granting, that the said effect may, nay ought to succeed in the Sea-waters, contained within their Vessels, subject to such like alterations, and especially in those that distend themselves long-wayes from West to East, which is the course that the motion of those same Vessels steereth? Now this is the most potent and primary cause of the ebbing and flowing, without the which no such effect would ensue. But because the particular accidents are many and various, that in several places and times are observed, which must of necessity have dependance