Ill 32' 



• . + 



43" 

 11 



— 8 



52 



. — 270 







201 24 



2 



201 23 



23 



201 24 



41 



834 Rutherfurd Photographic Measures. 



observed position angles have received a correction of -{-270 . This 

 will make them conform to the usual way of counting from the 

 North toward the point of greatest right ascension. Thus taking 

 as an example star 38, plate 5, we have : 



Corrected mean position angle . 

 Refraction (table II.) with changed sign . 

 Zero correction (table IV.) with changed sign 

 Corr. of -{-270°, with changed sign . 



Mean of observed position angles 

 Observed position angle East (table V.) 



Observed position angle West 



and in this way we can return to any of the observed position 

 angles of the Western impressions. 



Table VI. contains the final mean position angles, and the dis- 

 tances, reduced to seconds of arc by means of the scale value 

 28".oi24. These are followed by the differences of right ascension 

 and declination computed by means of the following formulae :* 



n = c sin w, m = a- cos tt, 



«' — «= [0.052857] n-f [4.4586] nm-\- [n 8.3872] n 3 -\- [9.2086] nm 2 , 

 *' — $=m-\- [w 4. 1047] n 2 + [n 8.8547] n 2 m. 



Table VIII. is a final catalogue of the Rutherfurd stars, the 

 position of 'j3 Cygni being given on the authority of AuwERS.f 

 The magnitudes are Argelander's. The precessions and secular 

 variations depend upon the constants of Struve,J and were com- 

 puted with the aid of Folie's tables. § 



It would not be easy to arrive at any quite definite information 

 as to the accuracy of the present measures. We have, of course, no 

 certain knowledge that the scale value determined from the Pleiades 

 remained unchanged up to 1875, wnen the j8 Cygni plates were 

 made. Yet it is fair to assume that a value which held true during 

 the whole period of Pleiades observations (1872, Jan. to 1874, Nov.) 

 had not materially changed a few months later. It is therefore 

 pertinent to inquire how nearly constant it remained during the 



* Ann. N. Y. Acad., vi, p. 317. f Publ. xiv, Astron. Gesellsch., p. 66. 

 \ Peters, Numerus Constans Nutationis, p. 195. Mem. de Saint-Peters- 

 bourg, 6 e Se>ie, t. iii, 1844. 



§ Douze Tables pour le Calcul des Reductions Stellaires, M6ni. Soc. Roy. 

 [883, supplement. 



