182 Dr. Gregory's Strictures on Don Rodriguez. 



commendation on him as a computer, or as an investi- 

 gator. 



The preceding remarks will suffice, I apprehend, to ren- 

 der manifest the probable object of Don Uodriguez's paper» 

 I shall now proceed to inquire how far the reasons assigned 

 by this gentleman bear hiin out in his attempt to throw 

 suspicion upon the operations of Colonel Mudge in mea- 

 suring an arc of the meriJian. The Don's paper, it is true, 

 is rather desultory and unconnected ; but 1 trust I shall 

 neither misrepresent him, nor do injustice to his arguments, 

 by endeavouring to reduce them to the following order. 



1. Colonel Mudiie's observations must be wrong some- 

 vherf , because his results do not correspop.d w ith those of 

 the French measurers. This is not positivelv affirmed, but 

 every where strongly implied : for Don R. assumes his 

 value of the radius of ihe earth's equator from the French 

 Itieasiirements and computations; and he takes it for 

 granted, that the fraction exhibiting the ratio of the difference 

 of the earth's axes to the major axis, technically termed the 

 compression , lies somewhere between those limits (-g4-5- and 

 •3-f-o) which a superficial observer 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 ike ratio of the earth's axes ; and 

 vhen in the course of any such admeasurements avowedly 

 Temarkable anomalies arise, it is a mere petitio principii to 

 conclude that there miist be some error in the astronomical 

 observations, because irregularities as great or greater than 

 those which the operations indicated result from computa- 

 tions resting upon a gratuitously assumed ratio. 



But some of the French operations at home, compared 

 with those at Peru, give about -j-i-g- 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 

 olservations. Don Rodriguez himself, when applying the 

 came lest to the French meridian, thereby detects irregu- 

 larities, and great ones too ; yet does not whisper the 

 gentlest hint that they were occasioned by inaccurate ob- 

 servations. Why not ? Because M. Mechain " handled 

 instruments with ^^rd^ai delicacy, and was possessed of p^- 

 euliar talents for this species of observation." So that a 

 g-atuitous assumption should suffice to render English ob-- 

 servalions doubtful, while it leaves the accuracy of French 



• Biot, Aitrvnomie Physique, torn. i. p. 159. 



ones 



