272 Mr Galbraith on the EngUsh Arc ofilie Meridian. 



fixed to the circle than in the comparatively slender tube at 

 present in use. The instrument would then be reversed by a 

 proper machine in the same manner as the transit instrument ; 

 while, from the cheapness of the materials, it would be far less 

 expensive. 



While these general objections are made to English instru- 

 ments, one would be justified in making still stronger to most 

 of the foreign. The French repeating circle, invented by 

 Borda, depends upon a principle of great ingenuity, though in 

 practice it does not equal the sanguine expectations of its 

 greatest admirers. There is a much greater want of stability 

 in its structure than in any of our instruments, which, perhaps, 

 might be improved by the suppression of some of their numer- 

 ous adjustments ; and though in the French arc of the meridian, 

 and in the New Trigonometrical Survey of France, under the 

 title, " Description Geometrique dela France," it has played a 

 very important part ; yet there are discrepancies in several of 

 the observations connected with some of these fine operations, 

 which would tend greatly to shake our confidence for extreme 

 precision in its final results, deduced from even thousands of 

 repetitions. In determining the latitude of the Observatory of 

 Saint Martin d'Angers, as recorded in the Description Geo- 

 metrique, Deuxieme Partie, page 499, Colonel Coraboeuf, with 

 a thu'teen-inch repeating circle of Gambey, from observations 

 on Palaris, at its upper transit north of the zenith, by about 

 40° 55', found the latitude to be . . 47° 28' 15".21 N. 

 By a Serpentis, 40" 29' S. of zenith, . 47 27 59 .41 N. 



Half sum or mean, .... 47° 28' 7".3i N. 

 which is accounted the true latitude. But there is a difference 

 between these results, amounting to no less than 15".8, one- 

 half of which, or 7".9 taken negatively, is reckoned the error 

 of the instrument at a zenith distance of about 40° 40'. 



Again, by /? Urste Minoris, at a zenith distance of about 

 27° 23' N. at its upper transit, the latitude by the same instru- 

 ment was 47° 28' 10".95 N. 



By Arcturus, with Z. D., 27° 23' S. it was 47 28 1 .41 N. 



Half sum or mean, .... 47^28' 0".95 N. 



