246 Mr. South' s observations of the apparent distances 



No. DCCXXXVI. continued. 



Measures of A C. 



Blackman-street ; July 4, 1824 ; Five- feet Equatorial. 



6th and 7 th magnitudes. 



Position =43° 16' sp 

 Distance = i' io".402 



5 Obs. I DifF. = 0° 1 3' ) 

 5 Obs. I DifF. = o".432 3 



Passy ; November 3, 1824 ; Seven-feet Equatorial. 

 6th and 7th magnitudes. 



Position = 43* 39' sp 

 Distance == i' 9".839 



5 Obs. 

 5 Obs. 



DifF. = 1° 40' ) 

 DifF. = i".635> 



Passy ; August 12, 1825 ; Seven-feet Equatorial. 



7J and 8th magnitudes. 



Position = 42° 39' sp I 5 Obs. I DifF. = 0° 31' ) Unsteady 

 Distance = i' io".022 | 5 Obs. | DifF. = i".75s 5 ^^steaay. 



Mean Result. 

 of A B. Position 57° 58' np (15 Obs.) ; 



Distance ii".777 (i5 Obs.) 



of AC. Position 43° n' sp (15 Obs.); 



Distance 1' io".o88 (15 Obs.) 



Epoch 1824.98. 



Sir W. Herschel has no measures of the positions of these 

 stars. The distance of A B he makes 11" 4/", agreeing pretty 

 well with the present ; while that of A C is stated by him at 

 59" 49'", a convincing proof of some cause of error in the 

 micrometer when opened to considerable distances, and which 

 has been already alluded to. What this cause of error may 

 have been, whether parallax, or the resistance of a spiral 

 steel spring straining the threads of the screw immoderately, 

 it is useless now to enquire ; but the whole tenor of the 

 observations goes to prove, that distances less than 20 or 30" 

 are not affected by it. (H.) 



