which relatively reſts in the Ship, will really and abſolutely move with the ſame velocity which the Ship has on the Earth. But if the Earth alſo moves, the true and abſolute motion of the body will ariſe, partly from the true motion of the Earth, in immovable ſpace; partly from the relative motion of the Ship on the Earth: and if the body moves alſo relatively in the Ship; its true motion will ariſe, partly from the true motion of the Earth, in immovable ſpace, and partly from the relative motions as well of the Ship on the Earth, as of the Body in the Ship; and from theſe relative motions, will ariſe the relative motion of the Body on the Earth. As if that part of the Earth where the Ship is, was truly mov'd toward the Eaſt, with a velocity of 10010 parts; while the Ship it ſelf with a freſh gale, and full ſails, is carry'd towards the Weſt, with a velocity exprſs'd by 10 of thoſe parts; but a Sailor walks in the Ship towards the East, with 1 part of the ſaid velocity: then the Sailor will be moved truly and abſolutely in immovable ſpace towards the East with a velocity of 10001 parts, and relatively on the Earth towards the Weſt, with a velocity of 9 of thoſe parts.
Abſolute time, in Aſtronomy, is diſtinguiſh'd from Relative, by the Equation or correction of the vulgar time. For the natural days are truly unequal, though they are commonly conſider'd as equal, and uſed for a meaſure of time: Aſtronomers correct this inequality for their more accurate deducing of the celeſtial motions. It may be, that there is no ſuch thing as an equable motion, whereby time may be accurately meaſured. All motions may be accelerated and retarded, but the True, or equable progreſs, of Abſolute time is liable to no change. The duration or perſeverance of the exiſtence of things remains the ſame, whether the mo-
