Zach on Repeating Circles. 357 



M. Mechain continued to make observations at the Royal 

 Observatory. In the months of July and August, 1799, he 

 observed the pole-star at its upper culmination, and in May 

 and June at its lo-wer culmination ; as also /3 Ui-s<^ Mino7-is 

 at its upper culmination, and in August and September at its 

 lower culmination. His tables give the following differences : 



By the pole-star upper culm. 



lower ditto 



Ey/3 UrscB Minor is upper ditto 



lower ditto 



Towards the end of the year 1796, M. Delambre set out for 

 Evaux. He there observed the zenith distances of the same 

 stars, with the same circles with which he had observed them 

 at Paris. His greatest differences then were : 



By the pole-star upper culm. 



lower ditto 



By/3 Ursce Mi7iorisuY>Y>&v ditto 



lower ditto 



We see here that the differences, according to M. Delambre, 

 are much greater than those of M. Mechain at Paris. Does 

 this arise fi-om the superior skill of this able astronomer, or 

 from his choosing those of his observations amongst which 

 there existed the greatest agreement ? It is impossible not to 

 suspect this, since he rejects observations by thousands. We 

 will also point out to our readers that M. Delambre frequently 

 uses the following expression ; as for instance, page 441, 

 " When I tried to unscrew the clamp, I found that it had loosened 

 of itself." This happened to him twice in five days, and we 

 are much astonished at it ; for we have no idea how iii an un- 

 interruptcd series of cross observations, such a clamp can loosen 

 itself after having been well screwed ; at least, such an acci- 

 dent has never occurred to us. 



M. Mechain was requested to go to Evaux to make obser- 

 vations conjointly with M. Delambre ; but this he always re- 

 fused to do. M. Borda wrote to him from Paris, " I cannot 



sen' 



* Errors of calculation frequently occur. For instance (p. 407), the ob- 

 „,.r\'ation of /3 Ursa: M'moris at its lower culmination, on the Dth of Sept. 

 179i), pivesas the true latitude 48° ."JO' 14,";n ; in the book it is marked 48° 

 SO" 16,"23. Many similar errors woidd be found on a revision of the cal- 

 culations. 



see 



