1658 Mechanic Powers. Book VIII.

or the Globe annext to the end of it, then either it mayſo be turned about by the Cylinder, that the ſame centre al-ways remains in the ſame point of the Axis, and then it ap-pears, that ſince the radius is ſhortned ſucceſſively, from thatGlobe is made à ſpiral motion of the ſecond kind, which iscompounded of circular motion only, for there may be per-ceived ſo many circular motions, although not perfect, as tEereare wreaths, or rather ſo many new determinations to newcircular motion, as there are conceived Radius one ſucceſſive-ly ſhorter than another; or, it may be ſo turn'd about by theCylinder, that the centre is changed at once, and then the mo-tion of the Globe. or the end of the Rope, will be a ſpiral mo-tion of the third kind, ſuch as may be conccived to be madeabout the Cone E F , from F in E, which appears to be mixtfrom a right motion of the centre, through the Axis of theCone , or Cylinder, and of many circular ones intelligible bySence; for it cannot truly be ſaid, that there are many circu-lar motions, ſince none makes a perfect circle, yea, no part ofthat ſpiral line is part of a circular line, but if it be taken as amall part, tis a right line from what hath been ſaid before;if as a compounded part, it conſiſts of many right lines, viz.of many Tangents , yet not of the ſame circle, but of divers cir-cles as appears.

Hence tis, that if a Cylinder be thicker, and a Rope of theſame length being put on it, tis eaſier and with leſs imprintedimpetus turn d about by the Cylinder; to wit, becauſe the partsof the circumference of the Cylinder are thoſe which reſiſt byimpulſe by a right line impreſt in the beginning, and by the im-pediment, or a certain reffection, they determine to new andney lines oftentimes; and by how inuch greater the circumfe-rence is, by ſo much the leſs frequent is that new deter minati-on, as appears from What has been ſaid, and ſo the leſſer 121.petus is deſtroyed, as that which is moved by a greater circleis leſs wearied or tyred.

Secondly, It appears why a Globe doth not aſcend, nor isturn'd about by a Cylinder, if the impetus be too weak in pro-portion to the thickpeſs of the Cylinder, or to the length ofthe Rope; for although it be ſo great that a right line could aſ-cend to that height, yet while it often ſuffers reſiſtance by re-Hections and new determinations, tis much abated.

Thirdly,