[ Sp3 ] 
Pine-apples, Extra& of a letter from William Ballard, Efq; on the culture ©f pine-apple^ 
p. 649. Method of raifing pine-apples in water, p. 649 — 652. 
Pitchy Sir Ifaac Newton the firft propofer of policing the metal for refle&ing telefcopes 
with it, p. 344. Suppofed to be the only fubftance in nature that is perfectly calcu- 
lated for that purpofe, p. 345—347. 
Pliny, his opinion concerning the propagation of bees, p. 16. 
Pocket electrometer, defcription of one, p. 599, 400. 
Pole . The furface of the earth at the pole for ever covered with fnovv, p. 764. n, 
Pole cat, (Viverra Futorius) a fpecies of it found in Africa, p. 40. 
Politics and religion of the Thibetians, p. 473 — 479. 
Portrait of Copernicus, prefented to the Royal Society by Dr. Wolf ; an account of it? 
p. 33. See Copernicus . A portrait of him in the great church at Thorn, p. 34. 
Portraits . See Painters . 
Precepts and tables for calculating any acceflible heights or depths from barometrical ob- 
fervations, p. 571 — -^9 7 . 
Pri/matic micrometer ; an account of a new inftrument fo called, for meafuring fmall 
angles, p. 799. See Micrometer, 
Problem (mathematical). Suppofe a given fpheroid, whilft revolving uniformly about its 
proper axis, with a given angular velocity, to be fuddenly urged by fome percuffive 
force to turn, with fome given angular velocity, about a diameter of its equator ; 
it is propofed to explain the rotatory motion of the fpheroid confequent to the irn- 
pulfe fo received, 283 — 288. 
Proportion, The general mathematical laws which regulate and extend proportion uni- 
verfally ; or, a method of comparing magnitudes of any kind together in all the 
poffible degrees of increafe and decreafe, p. 450 — 457.. 
Pump . See Air-pump,. 
Quantities (mathematical). A method of finding the value of an infinite feries of de 
creafing quantities of a certain form, when it converges too flowly to be fummed in 
the common way by the mere computation and addition, or fubtra&ion of fome of 
its initial terms, p. 187. Differential feries, p. 187—190. Of the convergency of 
the foregoing differential feries^ p. 190 — 19 1. Of the inveiligation of the foregoing 
differential feries, p. 191 — 194, Examples of the ufefuinefs of the foregoing diffe- 
rential feries in finding the values of infinite feriefes whole terms decreafe very 
flowly, p 194. Computations of the lengths of circular arcs by means of infinite 
ferieffes derived from their tangents, p. 194 — 199. Computation of an arch of 30 
degrees, p. 199 — 203. Computation of an arch of 45 degrees, p. 203 — 215. Com- 
putation of the feries which expreffes the time of the defcent of a pendulum through 
the arch of a circle, p. 215 — 230. 
