function OnMouseDown () {
     Fball1x = ball1.transform.position.x;
     Fball1y = ball1.transform.position.y;

     ball1.transform.position.x=ball2.transform.position.x;
     ball1.transform.position.y=ball2.transform.position.y;

     ball2.transform.position.x=Fball1x;
     ball2.transform.position.y=Fball1y;
    }