360 Zach on Repeatmg Circles. 



By/3 Ursa; Miiwris upper culm. 



lower ditto 



By ^ Urscc Mqjoris upper ditto 



lower ditto 



By Capricorniis 

 By /3 Geminorum 



Tlie fort of Montjouy is at the distance of only 1094 toises 

 fi'om Barcelona; indeed, of only 950 toises in the direction of 

 the meridian. In reducing the latitudes observed in these two 

 places to the same point, a difference appeared of 3", although 

 1728 observations had been made. This was the inexplicable 

 difference which was the torment of M. Mechain to the end of 

 his life, and as M. Delambre says (p. 617), the secret cause 

 "johich had produced that earnest and singular (? !) desire of 

 returning to Spain manifested by M. Mechaiji. 



It is curious to read in the second volume of the Base 

 Metrique (p. 617 et seq.) all the conjectures, all the liypothe- 

 ses started by M. Delambre, to explain this incomprehensible 

 difference of 3", and which, in fact, explain nothing at all. 



But among all these hypotheses, M. Delambre passes over, 

 or rather rejects, precisely that which, according to all likeli- 

 hood, is the only true one. He says, " that he is perfectly 

 convinced that the difference of 3" between Barcelona and 

 Montjouy, ought not to be imputed to the observer." We have 

 the same conviction ; but we think that it might, with great 

 justice, be imputed to the instruments. Of this M. Mechain 

 was firmly persuaded, and this persuasion made him so earnestly 

 desire to return to Spain ; and when he found that an attempt 

 was making to prevent his return, he wrote to M. Delambre ; 

 " If I had ever been able to take a decisive step, I should have 

 gone, and have begun entirely anew, without consulting any 

 body, and at my own expense" (p. 626). In another letter, in 

 which he again speaks of his anxieties, and of the causes of his 

 earnest desire of returning to Spain, he adds, " Have the good- 

 ness, I beg, to give this a moment's reflection ; to confer about 

 it with citizen Borda. I will take with me two circles, and two 

 months at the utmost will be sufficient for my purpose. I am 

 sure I know the met ns of avoiding many causes of errors and 

 uncertainties," &c. But M. Mechain received no other answer 

 than this — That his project of returning to Barcelona appeared 

 at once useless and impracticable, Sfc. 



In 1803, we procured from Paris the best repeating circles of 

 Lenoir, which were at that time so much spoken of and praised. 



The 



1 



