INDEX.

Fact, or focal Points of an Ellipsis, what, iii. 143.Focus, what, iii. 15. Why so called, iii. 16. Imagi-nary or virtual, what, iii. 21. Solar, what, iii. 21.Positive and negative, what, iii. 22. In double con-vex lens, Rule for finding, iii. 25.

Foot, Englilh, compared with Standards of diverseNations, iii. 293 n.

Force, relative, what, i, 22 n. Of Bodies in Motion,Controversy about, i. 241 n. Of the Moon and Sun,

ii. 106 n. Of the Air’s Repulsion, ii. 135 n. OfWind on the Sails of a Mill computed, ii. 215 n.Of Wind mathematically calculated by the Anemo-scope, ii. 211 n. Centripetal Law of, determined,

iii. 150 n. & Jeq. Projectile Ratio of, iii. 153 n.

Forces with which a Body is attracted on two Spheres,

i. 87 n. Two acting on a Projectile, i. 129. Cen-tral, i. 133—136. Centrifugal, what, i. 135. Cen-tripetal, what, i. 136. Of the Sun and Moon firrailing the Water, computed, ii. 102 n.

Forcing Pump, Construction of the common, ii. 56 n.Fountains , Hypotheses of, ii. ion. Origin from theSea, wrong, ii. 10 n. Two Principles of, ii. 11 n.Natural, accounted for from Pressure, ii. 20.Friffion, its Effect on a Machine, i. 170. Not pro-portional to the Quantity of Surface, but to theWeight of the incumbent Part, i. 179. Several Par-' Ciculars of, i. 179 n. How diminished in any Ma-chine, i. 182 n. Particularly in Wheels, i. 183 n.Fufion accounted for, i 34 n.

G,

f" y ffge, Description of, ii. 23.

■ GaiiLsan Telescope, the first invented, iii. 63.Galileo, Jupi er’s Satellites discovered by, iii. 23 n.Gates of a Lock, i. 162.

Gcnr.es, M. de, his Clock ascending en an inclined Plane,i. 201 n.

-Glass T ubes, Phænomena of capillary, i. 23 n. SeeCapillary. Drops, Phænomena of, i. 38 n. Read-ing, Nature of, iii. 38 n.

Glasses, different Properties of, in Reflexion, iii. 20 n.

Uni-