Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/57

Book I.

But we may ditinguih Ret and Motion, abolute and relative, one from the other by their Properties, Caues and Effects. It is a property of Ret, that bodies really at ret do ret in repect of one another. And therefore as it is poible, that in the remote regions of the fixed Stars, or perhaps far beyond them, there may be ome body abolutely at ret; but impoible to know from the poition of bodies to one another in our regions, whether any of thee do keep the ame poition to that remote body; it follows that abolute ret; cannot be determined from the poition of bodies in our regions.

It is a property of motion, that the parts, which retain given poitions to their wholes, do partake of the motions of thoe wholes. For all the parts of revolving bodies endeavour to recede from the axe of motion; and the impetus of bodies moving forwards, aries from the joint impetus of all the parts. Therefore, if urrounding bodies are mov'd, thoe that are relatively at ret within them, will partake of their motion. Upon which account, the true and abolute motion of a body cannot be determin'd by the tranlation of it from thoe which only eem to ret: For the external bodies ought not only to appear at ret, but to be really at ret. For otherwie, all included bodies, beide their tranlation from near the urrounding ones, partake likewie of their true motions; and tho' that tranlation was not made they would not be really at ret, but only eem to be o. For the urrounding bodies tand in the like relation to the urrounded, as the exterior part of a whole does to the interior, or as the hell does to the kernel; but, if the hell moves, the kernel will alo move, as being part of the whole, without any removal from near the hell. Rh