,,^ 2 Mr. Dalby’s Deduction of the 
Greenwich and Dunkirk, fig. i.), or the longitude of the point 
D, will be found by the common proportion which in a right- 
angled fpherical triangle determines an angle when the legs 
are given : this will be obvious by conceiving a fphere (of any 
magnitude) to be defcribed about W as a center. 
Hence, as rad. : cotang, angle HWD (i° 28' 44". 8) ::fine 
angle HWP (38° 31' 20") : cotang. 2° 22' 26% the incli- 
nation of the planes of the meridians PH, PD, or longitude 
of Dunkirk on this ellipfoid. And as the difference of meri- 
dians of Paris and Dunkirk is 2' 2 1 ".9 (for this will not be 
materially affefted by different hypothefes) the longitude of 
Paris will be 9 m. 2oi s. in time. The longitude of Dunkirk 
from Paris (2' 21 A 9) is the mean longitude deduced at p. 223. . 
(Vol. LXXX.), which is only i".i lefs than that given in the 
Connoijfance des Temps, 1788 . 
The method of computing the latitude of the point D (was 
it neceffary) is thus: as rad. : cofine DWH :: cofine HWP : 
cofine DWP ; and fince the point W in the axis PW is given, 
and alfo the angle DWP in the plane of the meridian PD (by 
the foregoing proportion), the point D will be determined by 
the properties of the ellipfe ; which in fa& is nothing more 
than finding the inclination of the vertical at the point D with 
the given line DW, which inclination added to the angle 
DWP, gives the co-latitude of the point D And hence may 
be evinced the truth of what is advanced at p. 199. (Vol. 
LXXX,), that if the value of an arc on a fpheroid, confidered 
as an arc of a great circle perpendicular to the meridian , be given ,j 
the longitude may be found by fpherical computation, but not the 
latitude. For conceive the arc HD to be perpendicular to the 
meridian at H, then the angle HWP would he the co- latitude 
