164 Dr. Maskelyne’s Obfervations on the Latitude 
truth at both feafons of the year, viz. by the unknown error 
of the affirmed right afcenfion of a, Aquilse ; but his right 
afcenfions inferred from his obferved zenith distances would be 
affeCted contrary ways at the two oppolite fealons of the year, 
by the unknown errors in the refraftions, parallaxes, latitude 
of the place, and obliquity of the ecliptic. Hence, the mean 
of the two corrections of the fun’s right alcenfion, found from 
the obferved declinations about the vernal and autumnal equi- 
nox, would be the true correction of the aflumed right afcen- 
fion of u. Aquilai ; and the difference of the fame corrections 
would, by an eafy calculation, Ihew how much the computed 
declinations were too great or too little for the truth, and con- 
fequently what the true declinations were, and what the true 
zenith diftance of the fun was, when in the equator, or the 
latitude of the place, on fuppohtion that Dr. Bradley’s re- 
fractions were truly ftated ; for any fmall uncertainty in the 
obliquity of the ecliptic, as llated by him, could not affeCt this 
refult, which was deduced equally from obfervations of the 
fun in north and fouth declination, when the fame error of the 
obliquity would affeCt the fun’s right afcenfions deduced from 
the obferved declinations contrary ways. I took the fun’s paral- 
lax from the 24th of my tables annexed to my obfervations, 
conftruCted upon a horizontal parallax S^Sq, which I had 
deduced from the obfervations of the firft tranfit of Venus, 
that in 1761, and differing infenfibly from 8 7/ |, which I de- 
duced from the obfervations of the total durations of the tranfit 
between the internal contaCts obferved at Wardhus and Ota- 
heite in 1 769, confequently more correCt than the horizontal 
parallax of io // j ufed by Dr. Bradley. It is alfo evident, 
that the true zenith diftance of the equator thus found, dimi- 
riifhed by Dr. Bradley’s mean refraCtion, will be the apparent 
7 zenith 
