

376 ASTRONOMICAL OBSERVATIONS MADE AT [47 



The observation of the reflection of the wires gave b + c or 6 c ; 

 thence c was obtained. This mode was adopted almost exclusively from 

 September 24, 1864, till the Instrument was finally dismounted. 



The coefficient for diurnal aberration, 0",19 = O s ,013, is, in every 

 case, incorporated with the Collimation error. 



Correction for Curvature of Star's path. 



When the object is not bisected precisely on the meridian a small 

 correction is necessary for curvature of path. 



For stars near the pole the correction (C] may be calculated from 

 the formula 



where A is the North Polar Distance, and 6 the hour angle. 



Differentiating, and expressing c?A in seconds of arc, we have 



-. 



'2 



So that, for the Polar Distance 



^ ft f) 



A + n", C= -T-J-, sin 2A sin 2 - + 2 cos 2A sin 2 -, n". 



sin i 2* Zt 



For Polaris, 



A = l25'+", C = [4-00842] sin 2 ^+[0-30050] sin 2 |.n". 



For 5 1 Cephei, 



A = 2 46' + 71", C = [4-29861] sin 5 ^+ [0'29900] sin 2 f . n". 



Zi & 



For 8 Urs. Min., 



A = 325' + w", C= [4-38991] sin 8 -+ [0'29793] sin 2 f.n". 



2 



For A. Urs. Min., 



A- 1 6' +n", <7=[3-89862] sin 2 f + [0-30071] sin 2 f . n". 



2 2 



