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XVI. The Longitudes of Dunkirk and Paris from Greenwich, 
deduced from the Triangular Meafurement in 1787, 1788, 
fuppofng the Earth to be an Ellipfoid. By Mr. Ifaac Dalby ; 
communicated by Charles Blagden, M. D. Sec. R. S. 
Read May 19, 1791. 
I N the account of the Trigonometrical Operation in 1787, 
1788, which is given in the Philofophical Tranfadtions, 
Vol. LXXX. after the diftance of Dunkirk from the meridian 
of Greenwich has been determined on a parallel to the perpen- 
dicular at Greenwich, its longitude is found by fpherical com- 
putation, on a fuppofition, that the furface of a fphere nearly 
coincides with that of the earth in an eaft and weft direction, 
where the operation was performed ; and the magnitude of this 
fphere, or which amounts to the fame thing, the value in parts 
of a degree, &c. of a meafured arc on its furface (for as fuclx 
the arc between the meridians of Botley Hill and Goudhurft 
naay be conlidered) has been determined by actual obfervation 
at two ftations nearly in the latitude of Dunkirk ; and this 
independent of any hypothefis which can fenfibly affedt the 
conclufion. The principles, though not ftridtly geometrical, 
admit of little objection ; and therefore, as much care was taken 
in obferving the angles at thefe ftations, upon which the direc- 
tions of the meridians depend, the longitude of Dunkirk (and 
confequently that of Paris) as given in the Table, Vol. LXXX. 
2 P- 232. 
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