134 . Mr, William Galbralth, on some 



inches diameter, or 8 inches radius both with regard to 

 astronomical and geodetical observations, while the latter 

 had the benefit of a zenith sector of 8 feet radius, and a 

 theodolite of 3 feet in diameter, both without the principle 

 of repetition adopted by Borda. Hence, it may in general 

 be concluded, that the principle of repetition employed in 

 one class of instruments was nearly equivalent in securing 

 accuracy of results to the advantage of large size, and the 

 superior power of the telescopes in the other. Hence, we 

 may also infer, that one of Mr. Troughton's objections to 

 the repeating circle, namely, that when the instrument has 

 a telescope of small power the observations are charged 

 with errors of vision which the repeating principle will 

 not cure, is not borne out by experience. Indeed we cannot 

 comprehend the notion why the errors of vision as well as 

 of division according to the usual doctrine of probabilities 

 are, if not destroyed, at least greatly diminished, by the 

 principle of repetition. MM. Lenoir and Fortin have 

 lately improved the movements of the repeating circle in 

 some respects according to Puissant, and Mr. Troughton 

 has given some of its parts a better position for diminishing 

 friction and insuring accuracy of motion, though on the 

 whole it is still complex in its construction, and, so long 

 as its peculiar repeating principle is retained, it cannot be 

 much simplified. The late M. Reichenbach, of Munich, 

 constructed repeating circles which for some time have 

 enjoyed great reputation, chiefly on account of the goodness 

 of the tangent and damping screws, and the accuracy of the 

 division. The superior telescope is also attached to a circle 

 turning with ease and precision within the graduated circle 

 and having their faces both in the same plane. 



On the recommendation of Laplace this artist constructed 

 a large repeating circle of this description for the Royal 

 Observatory at Paris. Whatever properties it may possess 

 yet it has been thought advisable to have also a large 

 mural circle on the principles of Mr. Troughton constructed 

 by Fortin, which the French express a hope will contribute 

 greatly to the advancement of astronomy. From these 

 circumstances it seems to be admitted that the powers of 

 the repeating circle have been overrated, and that the ad- 

 vantages derived from the repeating principle are in a great 



