[ 26 3 ] 
XLVIII. Concife Rules for computing the 
Fjfe&s of RefraBion and Parallax in va- 
rying the Apparent Diflance of the Moon 
from the Sun or a Star ; alfo an eafy Rule 
of Approximation for computing the D fi- 
ance of the Moon from a Star, the Lon- 
gitudes and Latitudes of both being given , 
with Demonflrations of the fame : By the 
Rev. Nevil Mafkelyne, A. M. Fellow of 
Trinity College, in the Univerfity of Cam- 
bridge, and F. R. R. 
Read Nov. 15, 1 H E following rules, excepting 
one, are the fame which 1 have 
already communicated to the Royal Society, but with- 
out demonftration, in a letter to the reverend Dr. 
Birch from St. Ilt-lcna, containing the refults of my 
obfervations of the distance of the Moon from the 
Sun and fixed ftars, taken in my voyage thither, for 
finding the longitude of the fhip from time to time; 
fince printed in Part II. Vol. LH. of the Philofophi- 
cal TranfaCtions for 1762. The two rules for the 
correction of refraCtion and parallax 1 have alfo 
fince communicated to the public in my Britifh Ma- 
riner’s Guide to the difcovery of longitude from like 
obfervations of the Moon ; and have added in the 
Preface a rule for computing a fecond but fmaller cor- 
rection of parrallax, neceffary on account of a fmall 
imperfection 
4 
