414 Zach on Repeating Circles. 



years without being submitted to calculation; and we there 

 said (p. 691), " that if the observations had been confined to 

 one star, as was the case at the measurement of the three de- 

 grees at Peru, it would have been quite as possible to have an 

 amplitude of an arc of the meridian of 50",04 as one of 58", 70; 

 and that consequently the effect of the attraction of the Sche- 

 hallien movmtain might have been either 3",5, or 7",8, a dif- 

 ference which would have completely absorbed all the effect 

 of the attraction which we found at Mont Mimet." 



It is clear from hence, that if instead of Reichenbach's 

 small circle we had used at Mont Mimet Sisson's great sector, 

 which Dr. Maskelyne used at the Schehallien mountain, the 

 censure of the English artist would have been quite as appli- 

 cable and as just. At the same time he will perceive that all 

 the reflections he has made on this subject, we had made be- 

 fore him ; and that we were not ignorant, as he seems to be- 

 lieve, that it was very probable we should obtain a result in a 

 direction contrary to that of the attraction. 



Again : let us see whether a three-foot repeating circle of 

 Reichenbach would have done its duty better. Open the Ef- 

 Jemeride Astronomiche di Milaiio for the year 1815, Appejidice, 

 p. 16 & seq., and you will see, in the observations made with 

 that instrument, anomalies which extend to five seconds. 

 The observations of the pole-star combined from month to 

 month also exhibit differences of two and three seconds. If, 

 then, we had carried this instrument to Mont Mimet, and 

 had observed there as we did at Notre Dame des Angcs, and 

 at Vile de Planter, three stars, during twelve days of the 

 months of July and August, we might have obtained for the 

 first twelve days of these two months the following compara- 

 tive table : 



Eph. of Milan 

 for 1815. 

 p. 19 

 p. 20 

 p. 24 

 p. 25 

 p. 33 

 p. 34 



By comparing this table with that which we have given above 

 (see Phil. Mag. page 363) of our little circle, it will be seen that 

 the anomalies of t'.iese two circles are precisely the same. 



It was not therefore quite so absurd as has been represented 

 to use a 12-inch repeating circle for a mere experiment of cu- 

 riosity of no importance, whilst the greatest astronomers and 

 geometricians of France had, before us, used instruments of 



the 



