384 Ruther^furd Photograijhic Pleasures. 



observed distance West without the need of publishing it. Take, 

 for example, Star 23, Plate 15. 



Corrected, mean, 60.4950 



Refraction -with sign changed, colnmn 4, — .0249 



Aberration with sign changed, column 5, -J-.0039 



Scale with sign changed, column 6, — .0098 



Tangent Correction with sign changed, Table IV, +.0013 



h ( East + AVest ), 60.4655 



East + West, , 120.9310 



East, column 3, 60.4660 



Diff. = West, observed distance, 60.4650 



In like manner column eight gives the East observed position 

 angle and the last column the corrected mean from which we may 

 similarly reproduce the West observed position angle. Using for 

 illustration the same star and plate : 



Corrected mean position angle 295° 43^ 38^' 



Refraction with sign changed. Table II -j- 6 



Zero Correction with sign changed. Table III — 18 17 



Correction of 270° with sign changed* — 270 o o 



\ ( East -r West) 25° 25' 27'' 



East + West 50 50 54 



East, column 8 25 24 22 



Dift'. = West, observed position angle 25 26 32 



In this way one may return to any of the observed distances or 

 position angles of the Western impressions. 



Table YI. contains the final mean of the position angles and the 

 means of the distances as given in Table V., but reduced to sec- 

 onds of arc by the scale value 28. "0124, which is the mean of the 

 scale values deduced from all the Pleiades plates. f The}' are fol- 

 lowed in columns six and seven by the differences of ri^ht ascen- 

 sion and declination derived by aid of the formul{^,| 



*o' 



* This con-ection is simj)ly to make the position angles agree with the usual 

 method of counting from the North Point towards the East. Ann. X. Y. 

 Acad. Sci., Vol. VI., p. 272. 



t Ann. N. Y. Acad. Sci., Vol. VI., p. 335. 



jAnn. N. Y. Acad. Sci., Vol. VI., p. 317, from which I have departed in 

 notation, somewhat, for the convenience of comijuting. 



