258 



dr. Gregory's strictures on don Rodriguez. 



Herschel's 

 observations 

 on double 

 stars, show the 

 reason of the 

 apparent ano- 

 maly, in Col. 

 M.'s case, and 

 make it ra- 

 ther a proof of 

 accuracy. 



Major Lamb- 

 ton's observa- 

 tions so warm- 

 ly commended 

 by Don R. ; 

 abound in 

 great discre- 

 pancies. 



reason that I can perceive, than, that if they had been em* 

 ployed, they would have given the latitude of Dunkirk about 

 a second Jess than the observations of the pole star gave it. 

 Let Don Rodriguez reflect upon this, and then repeat that the 

 French operations " merit the highest degree of confidence." 

 But this is not all. From p. 39 of the same Discours Prelimi- 

 naire, it appears that three stars only were selected by Mechain 

 at Montjouy, in consequence of the coincidence of the results 

 arising from them. Among the stars rejected, was K Ursce, 

 because different observations gave a difference of 4". So 

 that the French also detected an irregularity respecting this star. 

 They assign, however, a wrong reason for the fact j for they 

 attribute it to errors in Bradley's table of refractions, while 

 the truth is, that ? Ursae is a double star, by no means easy to 

 observe properly. Indeed, it appears, not only from the obser- 

 vations of Col. Mudge, &c. but from those of Dr. Herschel 

 (Phil. Trans, vol. lxxxii. New Abridgment, vol. xv.), that 

 both fjt Draconis and ? Ursae are double stars j that of the 

 former, the two constituent stars appear equal, both white, 

 and not easily distinguishable, and at the distance of 4 // . 35 

 from each other, mean measure; and that of the latter, the 

 two are considerably unequal, and the largest difficult to bisect. 

 Hence Herschel's observations completely confirm those of 

 our trigonometrical surveyors. See also the catalogues of 

 Wollaston and Bode. 



Let us next enquire how far Major Lambton's observations, 

 which Don Rodriguez also seems to delight in eulogizing, 

 deserve to be preferred to Colonel Mudge's. From p. 356, 

 vol. x. Asiatic Researches, we learn that the Major's observa- 

 tions upon a serpentis were 14, of which two were 5°57 / 3"'38 

 and 5° 56' 53'i' 98 furnishing a difference of 9"' 3 ; more than 

 double the difference that has been found in the English obser- 

 vations, of which the Don complains ! At p. 357, again we 

 have a register of 16 observations upon > Aquilae, of which 

 two differ by 6"' 77. At p. 358, we have 18 observations upon 

 Atair, of which two differ by 5' 1 ' 38. There are also some 

 other palpable differences in Major Lambton's results, as de- 

 duced from different stars. The greatest is between Atair and 

 Markab, being 5" 48. Atair, from the number and agreement 

 of its observations among themselves, should be correct in 



zenith 



