VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 67 



which produce the female larva. They are always in that portion of the cell from which the larva 

 issues. 9. The female larva. 10. The female pupa. 11. The same, with the lid opening, and 

 the insect protruding. 12. The female fly in its complete state. The last 5 figures are much 

 magnified. 



XFI. The Longitudes of Dunkirk and Paris from Greenwich, Deduced from the 

 Triangular Measurement in 1787, 1788, supposing the Earth to be an Ellip- 

 soid. By Mr. Isaac Daily, p. 236. 



In the account of the Trigonometrical Operation in 1787, 1/88, which is 

 given in the Philos. Trans, v. 80, after the distance of Diinkirlc from the me- 

 ridian of Greenwich has been determined on a parallel to the perpendicular at 

 Greenwich, its longitude is found by spherical computation, on a supposition, 

 that the surface of a sphere nearly coincides with that of the earth in an east 

 and west direction, where the operation was performed; and the magnitude of 

 this sphere, or which amounts to the same thing, the value in parts of a degree, 

 &c. of a measured arc on its surface (for as such the arc between the meridians 

 of Botley Hill and Goudhurst may be considered) has been determined by actual 

 observation at 2 stations nearly in the latitude of Dunkirk; and this independent 

 of any hypothesis which can sensibly affect the conclusion. The principles, 

 though not strictly geometrical, admit of little objection; and therefore, as much 

 care was taken in observing the angles at these stations, on which the directions 

 of the meridians depend, the longitude of Dunkirk, and consequently that of 

 Paris, as given in the table, must be nearly true, whatever may be the real 

 figure of the earth. But, it may be said, that the arc between the meridians of 

 Botley Hill and Goudhurst (I7'i) is too short to infer from observation the 

 value of the arc between the meridians of Greenwich and Dunkirk, amounting 

 to near a degree and a half, sufficiently accurate for finding the longitude to great 

 precision ; because it has been remarked in the appendix to the same volume, that 

 an error of 1", in either of the horizontal angles at the above stations, would 

 cause a variation of near 6" of a degree in the longitude of Dunkirk or Paris. 



M. Bouguer's spheroid agreeing nearly with the meridional measurements, it 

 was adopted for the purposes of latitude. But the degree perpendicular to the 

 meridian, in latitude 51° 6' 53", is found to be 6l248 fathoms, which falls short 

 of M. Bouguer's degree about 22 fathoms; therefore, supposing the directions of 

 the meridians to have been very accurately determined, the earth cannot be this 

 spheroid, notwithstanding the ingenious hypothesis respecting the curve of the 

 meridian. But it is also well known, that the measured degrees of latitude in 

 different places are inconsistent with an elliptical meridian: for, suppose an ellip- 

 soid to be determined with the degrees found at the equator and polar circle, the 

 computed degrees in middle latitudes will be much longer than the measured 

 ones, as it is well known; and the whole meridional arc between Greenwich and 



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