6o 6 Mr. Dalby's Remarks on Gen . Roy’s Account 
If the latitude of the point B was given, and the earth a 
fphere, the co-latitude BP and the obferved angles PBG = 
1 1 9 0 2\ / I3 /X .2, and PGB=6o° iy' if'.y, would give PG 
the co-latitude of G, and the angle BPG the difference of 
longitude of B and G. 
Taking a fphere whofe diameter is nearly a mean between 
thofe in M. Bouguer’s lpheroid, the length of a degree of a 
great circle is 60859,1 fathoms, and the latitude of B will be 
51 0 16' 4i x/ ,45; therefore BP = 38 3 43' 1 8 r *5 4 ; this, with 
the obferved angles at B and G, give PGZZ38 53" 6 '.72, and 
the angle BPG, or difference of longitude = 27' 36 ' *7 > there- 
fore in the right-angled fpherical triangle PRG, rad. : tang. GP 
:: cofine angle RPG : tang. 38° 53' 3" -4-7 = RP ; and rad. : fine 
GP :: fine RPG : fine iy / 2c/ = RG. 
P. 209. 1 . 9. for 51 0 1 6 / 46 7 put 51 0 16' 46 // , i . 
P. 213. CorreCt the title of this Article, by reading geo - 
detical meafurement for “ pole-far obfervations f in the firft 
line. 
P. 217. After the word “ meridian”, in the third line of 
Art. X. inftead of “ and alfo the differences of latitude and 
longitude have been obtained by very accurate obfervations of 
the pole-ftar made at certain Rations to the eaftward of Green- 
wich,”, read and alfo the difference of longitude between 
Botley Hill and Goudhurft have been obtained by obfervations 
of the pole-ftar. — A correction of this kind feems necefl'ary, 
becaufe the pole-ftar obfervations have not been ufed in finding 
the differences of latitude. From the directions of the meri- 
1 
dians at the above ftations, the value (in parts of a degree) of 
the meafured arc of a great circle, perpendicular to the meri- 
dian, has been determined ; hence the lengths of the degrees 
in the Table, p. 227. have ,been inferred. The diftances from 
± the 
