$5% 



dr. Gregory's strictures on don Rodriguez. 



V>ou K.'s 2d 

 reason refut- 

 ed. 



Former 

 measures do 

 not agree in 

 their results,; 



Don K. 

 iifirms. 



-h r'*34. Here the compression which agrees best with the 

 observations is more than double what it ought to be. If a 

 medium compression had been chosen, the errois at the several 

 station would have deviated still farther from the probable 

 errors of observation. Don Rodriguez will find this confirmed 

 by Puissant, Geodesie, pa. J 3/. 141, and by Laplace, Exposition 

 du Sysleme du Monde, Liv. i.eh. 12. After he has duly reflect- 

 ed upon the deductions of those philosophers, he will, perhaps, 

 be convinced, that he has been rather precipitate in taking the 

 French operations as a standard. 



But, secondly, this writer infers that there must be some error 

 in Colonel Mudge's observations, because they tend to shew 

 that the terrestrial spheroid is very irregular. All the measure- 

 ments " which have been hitherto made in the northern 

 hemisphere, are (he tells us) extremely satisfactory by their 

 agreement, and give us great reason to presume, that the general 

 level of the earth's surface is elliptical and very regularly so." 

 " There woulcinot have remained the smallest doubt respecting 

 the earth being flattened at the poles," but for the " measure- 

 ment performed in England." But " this measure alone would 

 lead to the supposition, that the earth, instead of being flattened 

 at the poles, is, in fact, more elevated at that part (the author 

 means those parts) than at the equator, or at least, that its surface 

 is not that of a regular solid." The degrees, in fact, increase 

 as the latitudes diminish, which, says Don Rodriguez, " excites 

 a suspicion of some incorrectness in the observations them- 

 selves ;" whereas, the only fair inference is, that an insular 

 situation is very ill fitted to promote the determination of the 

 figure of the earth. Let us see, however, how " satisfactory" 

 former measures have been " by their agreement " and how 

 completely they prove that the earth's surface is " very regularly" 

 elliptical. Lacaille's degree in lat. ^5° N. compared with 

 Bouguer's at the equator, gives for the compression -^-L-. The 

 degree in Maryland, with Bouguer's equatorial, gives -3--^. The 

 Spanish degree at the equator, with tne French degree lat. 45°, 

 gives -j-J-y. Boscovieh's Italian degree, lat. 43°, compared with 

 Bouguer's at the equator, gives ^. J T Bishop Horstey, by a 

 geometrical mean of iwelve different ellipticities, obtains ^fa** 

 Boscovich, taking a mean from all the measures of degrees, so 



as 



