DR. GREGORY S STRICTURES ON DON RODRIGUEZ. 25 1 



server would adopt as most suitable to the French operations. 

 Such assumptions, by the way, are neither consistent with fair 

 criticism nor with sound logic : for the grand object in measuring 

 arcs of meridians is to determine the ratio of the earth's axes $ 

 and when, in the course of any such admeasurements, avowedly 

 remarkable anomalies arise, it is a mere petitio principii to con- T j ie p renc |j 

 elude that there must be some error in the astronomical observa- operations 

 tions, because irregularities as great or greater than those l"^^ rregtt 

 which the operations indicated, result from computations rest- tatties. 

 ing upon a gratuitously assumed ratio. 



But some of the French operations at home, compared with 

 those at Peru, give about -j-i-^. for the compression*. Be it so. 

 That is no reason why any such ratio should be adopted, as the 

 test by which to try the accuracy of English observations. Don 

 Rodriguez himself, when applying the same test to the French 

 meridian, thereby detects irregularities, and great ones too j yet 

 does not whisper the gentlest hint that they were occasioned by 

 inaccurate observations. Why not ? Because M. Mechain 

 €< handled instruments with great delicacy, and was possessed 

 of peculiar talents for this species of observation." 80 that a 

 gratuitous assumption should suffice to render English observa- 

 tions doubtful, while it leaves the accuracy of French ones 

 unimpeached. To me it appears that a candid critic would, in 

 analogous circumstances, make analogous inferences ; and not 

 sift one class of results to the bottom, while he satisfies himself 

 with merely glancing at the surface of the other class. Had he 

 examined the French measures a little more minutely, he 

 would, instead of adopting them as his standard, have found that 

 they exhibit far too great irregularities to be entitled to that 

 honour. Taking the results of the operations ofDelambre and 

 Mechain, as subdivided naturally by the assumed stations at 

 Dunkirk, the Pantheon at Paris, Evaux, C^-ji^one, and 

 Mbntjouy, and applying to them the principle developed by 

 £egendre, in which, " the sum of the squares, of the erFoY9 is Some anoma* 

 made a minimum," the requisite compression is ~\- ; and even fvJn"h }C 

 then the deviations from what the theory would require are, at measures. 

 Dunkirk— 2"*23, that is, nearly 2$ decimal seconds j at the- 

 Pantheon, + 5"63 $ at Evaux, —4 '79 j and at Carcassone, 



* Biot. Astronomic Physique, lorn. i.'p. 15°. 



S 2 + 1"'34. 



