PARABOLOIDES

, Parabolas of the higher orders.——The equation for all curves of this kind being , the proportion of the area of any one to the complement of it to the circumscribing parallelogram, will be as m to n.|

PARACENTRIC Motion, denotes the space by which a revolving planet approaches nearer to, or recedes farther from, the sun, or centre of attraction.

Thus, if a planet in A move towards B; then is the Paracentric motion of that planet: where S is the place of the sun.

Paracentric Solicitation of Gravity, is the same as the Vis Centripeta; and is expressed by the line AL drawn from the point A, parallel to the ray SB (infinitely near SA), till it intersect the tangent BL.

PARALLACTIC Angle, called also simply PARALLAX, is the angle EST (last fig. above) made at the centre of a star, &c, by two lines, drawn, the one from the centre of the earth at T, and the other from its surface at E.—Or, which amounts to the same thing, the Parallactic angle, is the difference of the two angles CEA and BTA, under which the real and apparent distances from the zenith are seen.

The sines of the Parallactic angles ELT, EST, at the same or equal distances DS from the zenith, are in the reciprocal ratio of the distances, TL, and TS, from the centre of the earth.