CHAPTER II PHILOSOPHY OF GRAVITATION--( continued ) ART. 18 . GRAVITATION ATTRACTION 24 " 19 . UNIVERSALITY OF GRAVITATION 24 " 20 . DIRECTION OF THE FORCES 26 " 21 . PROPORTION OF THE FORCES 26 " 22 . LAW OF INVERSE SQUARES 27 " 23 . TERRESTRIAL GRAVITY 29 " 24 . CENTRIFUGAL FORCE 30 " 25 . KEPLER'S LAWS 32 " 26 . FIRST LAW OF KEPLER 33 " 27 . SECOND LAW OF KEPLER 36 " 28 . THIRD LAW OF KEPLER 37