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XXIII. IntroduEHon to two Papers of Mr . 
John Smeaton, F. R. S . ^ the Reverend 
Nevil Mafkelyne, B. Z). F. R. S. AJlrono- 
mer Royal. 
Read May 12, y | " 1 H E two following papers I received 
1 from my ingenious, and much 
efteemed friend, Mr. John Smeaton, with his defire, 
that I (hould communicate them to the Royal Society, 
if I thought they contained any hints conducive to 
the improvement of aftronomy. As the firft paper 
points out the time of obferving the menftrual paral- 
laxes of the planets in thofe circumftances in which 
they will be greateft, and at the fame time fhews how 
to obviate the error, which would otherwife arife from 
the inaccuracy of their theories (which muft necef- 
fatily be ufed in the calculation), by correcting them 
from other obfervations, made on purpofe, before and 
after the firft mentioned obfervations ; and the fecond 
paper gives a new and accurate method of obferving 
the places of the heavenly bodies out of the meridian, 
independent of refraCtion, I apprehend they will prove 
acceptable prefents to aftronomers. 
I (hall only add one other remark, that has been 
fuggefted to me from the perufal of Mr. Smeaton’s 
firft paper j that, as it is there propofed to find the 
dimenfions of the orbit defcribed by the revolution of 
the Earth about its common centre of gravity and the 
Moon’s, by means of the menftrual parallax of Mars, 
near his oppofition, or of Venus, near her conjunction 
1 ' with 
