INDEX. 513- 
Pot-ajh and pearl, effect of, in producing black, p. 51. 
Pov.hon water, an inquiry concerning the nature of its 
mineral elaftic fpirit, or air, p, 357. The ferruginous 
and abforbent earths contained in that water, how kept 
diftblved therein, p. 359. The elaftic fpirit not de- 
tained in it by the p re Hu re of the atmofphere, or any 
other external force, p. 360. The Pouhon water 
wholly decompounded when the elaftic fpirit is ex- 
pelled, p. 361. No volatile fpirit obtained in the 
decompofition of Pouhon water, except its mephitic- 
air, p. 362. Vide Mephitic Air. 
Preface to aftronomical obfervations by the miftionaries at 
Pekin, by the Aftronomer Royal, p. 31, 
Pregnancy , obfervations on, p.476, &c. Many received 
opinions refpecling it, groundlefs, p. 477. 
PreJJnre of the atmofphere. Animal bodies capable of 
bearing greater variations of it than the natural ones, 
without any inconvenience, p.348. 
Price, the Rev. Dr. on the inialubrity of marlhy fitua- 
tions, p. 96. 
Priefiley , the Rev. Dr, on the noxious quality of the 
effluvia of putrid marfhes, p. 90. Dr. Alexander’s 
opinion of them erroneous, p. 91. 
PROBLEMS, mathematical. To find the interfedlion of 
two logarithmics, which have a right line given in pofi- 
lion for their common afymptote, and their fubtangents 
•given in magnitude, an ordinate in each curve drawn 
at right angles with the common afymptote through 
a given point in it being alio given in magnitude, 
p. 278. 
The converfe of the foregoing, p. 282. 
Two logarithmics, interfering in a given point, having 
a right line given in pofition for their common afymp- 
tote and fubtangents ieverally given in magnitude, to 
find the point in the afymptote where an ordinate 
being drawn at right angles to meet both curves, the 
areas intercepted between the two curves, and the com- 
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