246 PHILOSOPHICAL TRANSACTIONS. [aNNO 178/. 



signing to each section the measured portion of the corresponding terrestrial arc 

 resultino- from the triangles of the meridian. Having made the necessary calcu- 

 lations for these stations, he then infers that from these data, with the latitude 

 of the Royal Observatory at Greenwich 51° 28' 40'', and that of Paris 

 48** 50' 14^ we shall have the latitudes of the several stations between Green- 

 wich and Perpignan, with their differences, or the celestial arcs comprehended 

 between them, as below. 



Stations. Latitudes. DifF. or celestial arcs. 



Greenwich Royal Observatory 51° 28' 40" 0'" ^o gg' 50" 52'" 



Point M near Dunkirk 51 1 49 8 



Paris Royal Observatory 48 50 14 2 11 35 8 



Bourges 47 5 4 41 1 45 9 19 



Rodes 44 21 13 36 2 43 51 5 



Pei-pignan (St. Jaumes) 42 42 2 8 1 39 1 1 28 



This latitude of Perpignan 42° 42' 2" 8'", is what results from the immediate 

 comparison of the lengths of the celestial arcs, as determined by the zenith dis- 

 tances of stars, taken with a sector of 6 feet radius, and where the observations 

 are so nearly consistent among themselves, as to leave little doubt of their ac- 

 curacy ; but in the 290th page of M. Cassini's book, so often quoted, as well as 

 in the J 70th page of his Description Geographique de la France, published in 

 1783, the latitude of Perpignan is given 42° 41' 55^'', which is 7" 8'" less than 

 that deduced from the observations, without any reason that we can perceive 

 being assigned for the reduction. 



Perpignan, the southernmost station of the meridian line extending from 

 Dunkirk through the whole kingdom of France, is situated at no great distance 

 from the bottom of the Pyrenean mountains, where that lofty range ends at 

 the Mediterranean sea. M. De La Caille was of opinion, that the plummet of 

 the s»3tor must have been affected by the attraction which it would suffer from 

 that cause ; a supposition which however has been doubted, since the observa- 

 tions made in this country on the attraction of Schehallien : for by these it ap- 

 peared that the effect, though sensible, was but small, even when the sector 

 was placed as near as possible to the opposite sides of the mountain. It is in- 

 deed true, that the Canigou, the highest of the Pyrenean range, being situated 

 obliquely to the meridian, and at a considerable distance from Perpignan, would 

 not probably occasion much deviation in the plummet ; yet, on the other hand, 

 when we compare the very trifling quantity of matter in Schehallien with the 

 immensity of the mass in the Pyrenees, in the direction of the meridian, I 

 cannot help being of M. De La Caille's opinion, that the plummet of the 

 sector would be sensibly affected, that is, it would be drawn to the southward 

 out of its perpendicular direction, and would thus give the zenith distance of the 

 pole, or any other northern star, too little, and consequently a latitude too 



