Zacti on Repeating Circlei. 413 



and with a three-foot meridian circle of Reichenbach? {Cor. 

 Ast. vol. ii. p. 52; and vol. v. p. 499.) 



We might accumulate these questions and show that this 

 modest little 12-inch circle, so convenient and so trans- 

 portable, has rendered similar services at Verona, at Venice, 

 at Genoa, at Rimini, at Florence, at Pisa, at Lucca, at Naples, 

 &c. &c. 



Now we will ask, in the last place, with what other instru- 

 ment has so much ever been effected, and in so short a time ? 

 Could it have been accomplished with sectors of twelve and 

 fifteen feet ? With quadrants of eight feet ? With meridian 

 circles of eight feet ? We have, we trust, said enough to de- 

 monstrate, that our pygmy may enter the field with these mag- 

 nificent colossuses, and to justify ourselves for having admitted 

 it to the honour of the experiment in which we used it at 

 Marseilles. 



We have shown in the course of the present letter, that the 

 greatest differences between the observations made with our 

 12-inch repeating circle never exceeded three or four seconds. 

 Let us see whether the great instruments have succeeded bet- 

 ter, and let us first cast an eye over the observations of Gen. 

 Muclge, made with one of Ramsden's most perfect 12-foot 

 sectors. We shall find that in spite of the beauty and the 

 excellence of this magnificent sector, constructed by one of the 

 greatest artists of England, in spite of all the precautions and 

 all the skill of so adroit and experienced an observer as General 

 Muclge, he could not avoid anomalies to the extent of four 

 seconds. Don Rodriguez, in his paper printed in the Philo- 

 sophical Transactions, goes still further, and suspects an abso- 

 lute error of five seconds in the latitude of Arbiuy, " in spite 

 of the goodness of the instrument and of the skill and care of the 

 observer." In another passage he says : " It must, however, 

 be acknowledged that no reproach attaches to the greater 

 number of observers ; they have done all in their power ; but 

 in general too much confidence has been placed in the good- 

 ness of their instruments." 



Let us see whether the ten-foot sector of Sisson, with which 

 Dr. Maskelyne determined the attraction of the Schehallien, 

 would have done us better service, if we had made use of it, 

 instead of our own little circle, to determine the attraction of 

 Mont Mimet. The Doctor made with this instrument 337 

 observations, but of these he calculated only 40 ; we calculated 

 them all, and we found that the greatest differences they con- 

 tained extended to eight seconds. 



In our work U Attraction des Montagnes, we gave a table 

 of all those observations which had been left for nearly forty 



years 



