128 PHILOSOPHICAL TRANSACTIONS. [aNNO 1737. 



ence of longitude of the astronomical tower at Copenhagen and of Uraniburg 

 in the Isle of Huen. With this intent, in the month of April 1720, M. De 

 Lisle went some distance from Paris southward, to the places which he judged 

 most proper for the purpose ; but his design was not then executed, for want 

 of assistance, and for other reasons, which he passes in silence. Since that 

 time, he found that the Marquis Poleni had hit upon the same thought ; as 

 may be seen in his letter to the Abbot Grandi, dated in November 1724. 



The decision of this famous question, of the figure of the earth, had stopped 

 there, when in the year 1733, the minister of France having thought it neces- 

 sary to construct an exact map of the whole kingdom ; and being informed, 

 that the work could not be better carried on, than by the astronomers of the 

 Royal Academy of Sciences, applied to M. Cassini on that head ; who was of 

 opinion, that, to execute it with the utmost exactitude, the same method ought 

 to be employed as for the meridian, by taking through the whole extent of the 

 kingdom, triangles connected by means of objects seen successively, one from 

 another, &c. This project of making a map of France by such triangles, had 

 been already offered to M. Colbert, by Mons. Picart, in 168], but was not 

 then executed. However, M. Cassini proposed, that these triangles should be 

 begun in a direction perpendicular to the meridian ; in order to render these 

 operations of service towards the decision of the earth's figure, pursuant to the 

 method spoken of above : and M. Cassini, having in person undertaken these 

 operations, and having carried them that same year, 1733, from Paris to St. 

 Malo, whose longitude from Paris M. Picart had observed in 168I ; the rela- 

 tions of the degrees on the meridian and parallel, were found to be such as 

 were required in the hypothesis of the earth lengthened at the poles, and even 

 more lengthened than Cassini had determined in 17I8. For instead of the 

 diminution of a 6oth part for each degree of the parallel, which M. De Lisle 

 had found according to the earth's figure, as determined by Cassini in 17 18, he 

 deduced from his operations in 1733, a diminution of the 36th part of each 

 degree. 



It is true, that M. Cassini, in the account he gave of this determination at 

 the public meeting of November 14, 1733, does not give it as entirely certain; 

 because the longitude of St. Malo, with regard to Paris, was collected from one 

 observation only of Jupiter's first satellite, in which there may possibly be some 

 error : but at least M. Cassini seems certain, that there is a very considerable 

 diminution in the degrees of the parallel of Paris, which confirms his opinion 

 of the earth's being longest at the poles. This we are likely to have a better 

 assurance of hereafter, as we are informed that this measurement of the parallel 

 of Paris, is carrying on in France by M. Cassini's sons, M. Maraldi's nephew. 



