Ninthly, in art. 19 of the same chapter, I have shown, that _whatsoever is at rest will always be at rest, unless there be some other body besides it, which by getting into its place suffers it no longer to remain at rest_. And that _whatsoever is moved, will always be moved, unless there be some other body besides it, which hinders its motion_. Tenthly, in chap. IX. art. 7, I have demonstrated, that _when any body is moved which was formerly at rest, the immediate efficient cause of that motion is in some other moved and contiguous body_. Eleventhly, I have shown in the same place, that _whatsoever is moved, will always be moved in the same way, and with the same swiftness, if it be not hindered by some other moved and contiguous body_. [Sidenote: Other principles added to them.] 2. To which principles I shall here add those that follow. First, I define ENDEAVOUR _to be motion made in less space and time than can be given_; that is, _less than can be determined or assigned by exposition or number_; that is, _motion made through the length of a point, and in an instant or point of time_. For the explaining of which definition it must be remembered, that by a point is not to be understood that which has no quantity, or which cannot by any means be divided; for there is no such thing in nature; but that, whose quantity is not at all considered, that is, whereof neither quantity nor any part is computed in demonstration; so that a point is not to be taken for an indivisible, but for an undivided thing; as also an instant is to be taken for an undivided, and not for an indivisible time. In like manner, endeavour is to be conceived as motion; but so as that neither the quantity of the time in which, nor of the line in which it is made, may in demonstration be at all brought into comparison with the quantity of that time, or of that line of which it is a part. And yet, as a point may be compared with a point, so one endeavour may be compared with another endeavour, and one may be found to be greater or less than another. For if the vertical points of two angles be compared, they will be equal or unequal in the same proportion which the angles themselves have to one another. Or if a strait line cut many circumferences of concentric circles, the inequality of the points of intersection will be in the same proportion which the perimeters have to one another. And in the same manner, if two motions begin and end both together, their endeavours will be equal or unequal, according to the proportion of their velocities; as we see a bullet of lead descend with greater endeavour than a ball of wool.