362 



Zacli on Repeating CircXes. 



In 1809 we passed through Milan. We there made, with 

 tlie same circle of Reichenbach with which we had made our 

 experiments at Munich, several observations at the Imperial 

 Observatoiy of Brera ; among others, that of the summer sol- 

 stice. M. le Chevalier de Cesaris, the director of that obser- 

 vatoiy, made similar observations with the superb eight-lbot 

 mural quadrant of Ramsden. We had agreed to compare 

 every day the apparent altitudes of the sun, which we observed 

 with our respective instruments ; this comparison must conse- 

 quently have given the eri'ors of collimation of the mural circle, 

 since it is well kno^vn that altitudes observed with the repeat- 

 ing circle are exempt from them. The following is the result : 



Errors of Collimation of the Mural Circle. 



1809, June 11 -H 0, 



13. 

 14. 

 15. 

 17. 



18. 



.- 4, 

 .- 0, 

 .- 3, 

 .- 3, 

 .- 2, 



1809, June 19. 

 21. 

 22. 

 23. 

 25. 



.- 4,"0 



,- 7, 3 



.- 6, 4 



.- 3, 4 



.- 3, 4 



These errors of collimation ought to be every day the same ; 

 nevertheless, they present anomalies which extend from zero 

 to seven seconds. Tliese irregularities ought, without doubt, 

 to be distributed between the two observations ; but to which 

 of these instruments ought the greater part to be assigned, to 

 the dwarf, or to the colossal instrument ? The question is easy 

 to decide. It was only necessary to compare the latitudes given 

 by the two instruments. We have calculated them as follows : 



The greatest difference in the mural circle of Ramsden amounts 

 to 7", whilst in the repeating circle it amounts only to 1",7, 



In 



