[ 35 6 ] 
on this fubjedt, we fhall probably, at laft, be in- 
debted to obfervations of the moon’s parallax for the 
bed determination of it: for though the earth affords 
but a fmall bafe at the moon, yet, by repeating 
thefe trials, and comparing their refults, we may 
hope to attain that degree of exadtnefs, which we 
could never expedt from fewer obfervations. 
As I look upon the fpecies of obfervations here 
fpoken of to be of very important ufe for the im- 
provement of aftronomy and geography, and as fuch 
defire to recommend the practice of them, efpecially 
to thofe who may have occafion to vifit countries of 
diftant latitudes; I fhall briefly mention fuch further 
particulars, which the experience I have had, and 
my attention have fuggefted to me, the obfervance 
of which may conduce to the greater accuracy, as 
well of the obfervations, as of the confequences to be 
deduced from them. 
I apprehend the ufe of a polar axis to be very ne- 
ceflary for rightly managing the telefcope, as well 
for finding what ftar it is proper to compare the 
moon with, as for -preferving the pofition of the 
wires unvaried, after their adjuflment. A very 
nice and exadt polar axis is not requifite ; but a cheap 
one, and fuch an one as may eafily be provided, will 
fuffice. Mine was formed by a brafs focket, making 
an angle with the horizontal top of the ftand equal 
to 1 6° or the latitude of the place, receiving the 
brafs cylindrical fupport of the telefcope, inftead of 
the perpendicular focket of the common ftand : and 
the telefcope was firmly confined in the focket bv 
a pointed fcrew which pafled through one fide of 
the 
