[ 181 ] 



XXIX. The Ophnons cf Dr. Thomson a?id the Chevalier De- 

 LAMBRE, in reference to Don Rodriguez's A7n7nadversions 

 cm the Tricronometricai Survey, contrasted. By Olinthus 

 Gregory, LL.D. of the Royal Military Academy. 



To Mr. Tilloch. 



Sir, Jf Dr. Thomson had not, with a species of moderation 

 and candour, which 1 suppose he indulges that it may be seen 

 with what propriety he assumes the character of a genuine phi- 

 losopher, positively shut his " Annals" against any reply I might 

 be inclined to make to his animadversions, and even to his 

 qiieslions* , I should not have troubled you with an additional 

 communication, on a subject now so well understood, and cor- 

 rectly appreciated, as Don Rodriguez's remarks on the " Trigo- 

 nometrical Survey," 



On that subject I took up my pen unwillingly ; but it is gra- 

 tifying to know, at the end of a year and a half, that on the one 

 hand the only person who has put his name to any public cen- 

 sure of my undertaking, is one who is obviously ignorant of the 

 matter respecting which he ventures to obtrude his sentiments 

 upon the v.orld ; whiie, on the other hand, the justice of my 

 strictures has been acknowledged by all competent judges, and 

 has indeed been confirmed bv the most distinguished astrono- 

 mer now living in Europe. 



The readers of No. 1 71) of the Philosophical Magazine, and 

 No. 159 of the Journal, will recollect that I there attempted, 

 and I hope successfully, to refute everv argument advanced by 

 Don Rodriguez to prove the incorrectness of Colonel Mudge's 

 observations at Arbury Hill ; that 1 have proved that the Don's 

 opinions as to the regular ellipticity of the terrestrial meridians, 

 and indeed as to the subject generally, run counter to those of 

 the greatest philosophers in Europe ; that an error of A\ seconds 

 could not arise from Xhe. fixing, the construction, or the use of 

 the instruments employed ; and that, so far from there being an 

 error of that magnitude either at Arbury Hill or Shanklin Bea- 

 con (the Dunnose station), there cannot possibly be one of even 

 half a second, unless there be a corresponding or greater error in 

 the series of observations for years at the fixed observatories of 

 Blenheim and Portsmouth. 



Notwithstanding this, however. Dr. Thomson, as if to con- 

 vince the world how profoimdly he is conversant with such topics, 

 atfirms that ^' well-founded dovhts may remain on the matter," 

 and that " the j)oint can only be settled by repeating the ob- 



* See Thomson's Annals, No. IQ, pnge 286. 



• M 'S servations : " 



