What is "paracentric motion"

paracentric \par`a*cen"tric\ (p[a^]r`[.a]*s[e^]n"tr[i^]k), paracentrical \par`a*cen"tric*al\ (p[a^]r`[.a]*s[e^]n"tr[i^]*kal), a. [Pref. para- + centric, -ical: cf. F. paracentrique.] Deviating from circularity; changing the distance from a center.

Paracentric curve (Math.), a curve having the property that, when its plane is placed vertically, a body descending along it, by the force of gravity, will approach to, or recede from, a fixed point or center, by equal distances in equal times; -- called also a paracentric.

Paracentric motion or Paracentric velocity, the motion or velocity of a revolving body, such as a planet, by which it approaches to, or recedes from, the center, without reference to its motion in space, or to its motion as reckoned in any other direction.