the Trigonometrical Operation . 2 o 3 
the Rations, by adlual obfervations of the zenith difiances of 
fiars, which, with the very beft inftrurnents hitherto ufed for 
that purpofe, could not have been done nearer than about \ /f 
of an angle in the heavens, anfwering in thefe parts to 101 feet 
on the furface of the earth. Even if we could have been fupplied 
with a fedor fo far furpafiing the old ones' (fuch perhaps as Mr, 
Ramsden may hereafter invent) that would have given zenith 
diftances to one- tenth part of a fecond, or about ten feet on the 
furface of the earth, the .application of it in our operation 
would have been mere lofs of time : for the Aftronomer Royal 
having fettled the latitude of Greenwich 51 0 28' 40"; to 
within lefs than half a fecond of the truth ; and the geodetical 
fituation of each Ration of our feries being determined fo accu- 
rately with regard to that point, as to leave no where an uncer- 
tainty of more than one or two feet; we have thereby been 
able to determine the relative latitudes to a fmall fraction of a 
fecond. Here, however, it is to be underftood, that we have 
adhered to M. Bouguer’s fcale, as anfwering almofi exactly in 
the narrow fpace of 26' 51", or thereabout, of latitude be- 
tween Greenwich and M, to which our operations have been 
confined. 
That this mode of fettling the latitudes of our Rations is 
extremely accurate, will more fully appear from the following 
confiderations. In the general computation of fpherical tri- 
angles, a fphere whofe diameter is a mean between the longeR 
and fhorteft of M. Bouguer’s fpheroid has been adopted, be- 
caufe it was obvious, that in our latitudes the degree of fuch a 
fphere could not differ fenfibly from the mean degree of the 
fpheroid. Thus the degree of the fphere 60859.1 fathoms 
anfwers (as may be perceived by confulting the table in the 
Paper of 1 787) the degree of the meridian on the fpheroid in 
D d 2 the 
