t 458 ] 
N. 
New'on, Sirlfaac. S zt Velocity, of 1 he Rays of Light , Leibnitz. 
Nitrous air. See Saline L!u\ 'flances, Fleftricity. 
No/let, Abbe. Ilis excellent method of difeovering the errors occaiioned by the inequa- 
lities on the inner furfacc of the glafs of thermometers, p. 79. 
O. 
Optics. Too much has hitherto been taken for granted in that fcience, p. 91. The 
pofition, “ that we gain nothing by magnifying too much ,” confidered. p. 92. et feq. 
Superiority of the fingle eye-glals to the double, in point of light and diitinttnefs, 
p. 95. 
Optic pencil. Obfervations on, p. 96. 
P. 
Parallax of the fixed ftars. See Fixed Stars. 
Perpetual motion. The idea of, a contradiction in terms, p. 3 ^4. 
Petit , Mr. See Sulphur. 
Phlogiflnn. See Saline Subfiances. The nature of it explained, p. 195. Can never be 
produced in a concrete ftate, fingle and uncombined with other fubilances, ibid. 
The caufes of inflammable air and fpeciflc fire, which are different ftates of phlo- 
gifton, explained, according to die difeoveries of Dr. Black, p. 196. See Fixed 
Air , Inflammable Air. 
Population. From Mr. Wales’s “ Inquiry into the prefent State of it in England and 
Wales,” and different numbers of thefe Tranfa&ions, appears to be in a general 
and progrefiive ftate of improvement, p. 35. 
Prcfents. Lift of, p.445. 
Prieflley, Dr. See Saline Subflanccs. By his new analyfis has produced the volatile 
alkali free from the aerial acid and water in the form of air, p. 19 1. See hflamna - 
lit air « 
R. 
• t 
Rain. Account of a new kind of rain at Mount Etna, by the Count de Gioeni, i. 
Various conjedtures concerning the caufe of, ibid. Methods of analyiing it, to 
determine its origin, ii, iii. Which appears to be volcanic, iii. Not hurtful to 
animals or vegetables, iv. Its great extent accounted for, ibid. Table of the 
quantity of rain which fell near Barrowby near Leeds, by George Lloyd, Efq. p. 
7 l * 
