INDEX.

in a Circle to that in a conic Section determined, iii.I 53 n-

Rationale of fifty Experiments on the Air-Pump, ii.155 n. & seq.

Rays , different Refrangibility of, ii. 301 fcf seq. Re-fracted, appear in th-ir proper Colours, ii. 312. Se-paration of by a Lens, ii. 314. Particular Degreeof Refraction in each, ii. 315 n. Parallel, what,iii. 8. Converging, what, iii. 10. Diverging,what, iii. 13. Parallel, on a plane Speculum, howreflected, iii. 21.

Reading- Glass, Nature of, iii. 38. General Use of,to what owing, iii. 41.

Reciprocating Springs, fee Springs.

Reduplication of Sound, fee Sound.

ReJleBing Telescope, see Telescope. Microscope, seeMicroscope.

Resection and Inflection of Light accounted for, i. 38 n.Of Light, its Cause, ii. 33611. Particular Mannerof unknown, ibid. See Light.

Refraction , the particular Degree of every Species ofRays, ii. 315 n. To what owing, ii. 336 n. InCurves of the conic Sections demonstrated, iii. 18 n.See Light.

Refractive Power of the Air how determined, ii. 309 n.its seq.

Refrangibility of the Sun’s Light accounted for, ii. 313n. Of several intermediate Rays determined, ii.Z2i n.

Refrangible Rays, what, iii. 72 n. See Rays.

Regular Bodies, i. 9 n.

Relative Force, what, i. 22 n. Weight of Bodies,what, i. 85 n. Motion, what, i. 88, 89 n.Renitency of the Air, what, ii. 128.

Repulsion , what, i. 13. Difference between it and At-traction, ibid. n. In the Air, its Force, ii. 135 n.Resitutive Force of a String, what, ii. 236 n.

Retarded Motion, what, i. 89.

Retina , what, iii. 29.

Rhumb- Line, what, iii. 312 n.

Ring of Saturn described, iii. 124. Sometimes ob-served double, iii. 128 n.

Rivers, great, how formed, ii. 15 n.