XXVI. _That kicking up the Heel behind, and twisting round upon one Leg, is fine Scating._ There are two Methods of Scating, one is made Use of for the Sake of Expedition and Conveyance from Place to Place, and is practised by the Boors or Peasants in Holland; the other is calculated entirely for Amusement, and answers the End of _Shining_ upon the Ice, and therefore is suited for Gentlemen near Towns upon Canals, and broad Pieces of Water. The first of these Methods is performed by throwing the Body into such an erect Posture inclining a little upon the Outside of the Scate, and drawing in the Hip gradually, as will describe small Curve upon the Ice; this Practice of Scating eases the Inside of the Thigh, and rests it in such a Manner as to allow it Time to regain Strength for the next Stroke, and therefore is very useful in long Journies; or else as to the Article of Swiftness, a straight Line will carry a Person on faster than a Curve, because while he is describing a Curve he has more Ground to run over. The other Method of Scating, which is known in England by the Name of Rolling, is done upon the same Principle as the former, only as you have no Occasion for Expedition, you have an Opportunity of dweling longer upon your Strokes, and your Time; by which Means, instead of describing a small Curve, you describe a large one. It will be necessary to explain the Cause of this Motion, before we can make the Reader sensible of what we intend to say. All Bodies that are put into Motion upon the Surface of the Earth, are acted upon by two Forces; namely, a Projectile Force and a Centripetal Force. The Projectile Force is that which is given it by the Hand or Strength of any Person, and the Centripetal Force is that which causes all Bodies to seek the Center of the Earth. For Instance, when a Stone is cast into the Air to any Distance, the Reason why it does not move on to Eternity without stopping (as it ought to do by the Principles of Mechanics) is, because the Centripetal Force keeps continually acting upon it, till it has pulled it down to the Ground again: This serves to explain what is meant by a Centripetal Force.