[ §91 3 
like care and accuracy, which he has uied : for, as 
Dr. Bradley has himlelf remarked,, where any liars 
are remote from the zenith, the uncertainties oi le- 
fra&ion, and the irregular motions of the air, become 
fo great, as to take away from us all hopes of ob- 
ferving them to an equal degree of exadtnels. 
The particular Har, which, I propofe, ihould be 
carefully obferved, with a view of difcovering its an- 
nual parallax, if fenfible, is Sirius, the brighteft of 
all the ftars in the firmament, and which is there- 
fore, probably, the neareft to us of them all. With 
us, this ftar pafiTes the meridian, at the altitude of 
a 2°, where the refradfions are too irregular to admit 
of our difcovering a very minute quantity, by obfer- 
vation : but, at the ifland of St. Helena, Sirius paffes 
only half a degree fouth of the zenith ; and, on this 
account, I have, for fome time, looked upon that as 
the moft proper place to make obfervations at, for 
this purpofe. 
I {hall now beg leave, with great deference, to lay 
before you a particular argument, which has, for 
thefe two years, induced me to think it piobable, 
that the annual parallax of Sirius is not fo fmall, as 
to elude the nice difcernment of our modern aftro- 
nomers ; and (hall be glad to be determined by your 
opinion, whether it affords a fufficient prefumption 
to us, to undertake a careful and affiduous feries of 
obfervations of the distances of Sinus, fiom the 
zenith of the ifland of St. Helena. _ This argument 
is drawn from an examination, which I have made, 
of the obfervations of the zenith djftances of Sirius, 
taken at the cape of Good Hope, in the years 175* 
and 175a, by that excellent aftronomer, and diligent 
Vol. LI. 5 y obferver, 
