the Trigonometrical Operation. 2 g 
any other country. Bur, by proceeding with the work in the 
iame manner as it has been begun, with more perfed inftru- 
ments than have heretofore been ufed, and feme of thefe ap- 
plied in a new way, a map of the Britilh Mantis will at length 
be obtained, greatly fuperior in point of accuracy to any that 
is now extant. 
One additional inftrument would certainly be wanted, that 
is, a zenith fedlor for the determination of the latitudes, when 
the operation came to be extended to any confiderable diftance 
from the parallel of Greenwich. But this would not be ne- 
ceflary at firft ; while fuch a one is preparing by Mr. Rams- 
DiiN, and whicn he will no doubt render the compleateft thing 
of the kind, the operation fhould be continued in the parallel 
of Greenwich, or m the perpendicular of its meridian, quite 
to the weftern fide of the ifiand in the manner following. 
In more than one place of this Paper we have had occafion to 
exprefs our regret, that the recent feries of triangles did not afford 
diftances fufficiently great between points reciprocally vifible, 
for the bell application of the pole-ftar obfervations, to the de- 
termination of the differences of longitude. It Is believed, 
that the obfervations themfelves are extremely near the truth, 
but not wholly free from error ; therefore, whatever this may 
amount to, on double or triple the diftance it would certainly 
be reduced to one-half or one-third part. 
Shooter’s Hill, and Nettlebed Heights on the eaftern fkirt of 
Oxfordfliire, are reciprocally vifible at the diftance of about 
forty-fix or forty-feven miles from each other. Nettlebed 
Heights, and a thin clump of trees on the Gioucefterlhire 
range of hills, called Paul s Ppljile, about two miles weltward 
from Frog Mill, on the left-hand fide of the road leading from 
tnence to Gloucefter, may likewife be feen from each other at 
Y 
the 
