180 Prof. C. Pritchard. On the Capacities of two [May 3, 



focus mirror, and that with an exposure of one hour no fainter star 

 than the fifteenth magnitude leaves a trace at all discernible on the 

 photographic film. 



In the following tables are given the results of the preceding 

 formulas as applied to stars whose magnitudes have been determined 

 by the wedge photometer, and recorded in the ' TJranometria Nova 

 Oxoniensis.' In the first column is given the designation of the star 

 in the Pleiades, adopted by Bessel. The remaining columns speak for 

 themselves. 



Table 1. — Exposure 5 minutes. Mirror -^-inch. 



Star's 

 designation. 



Measured 

 diameter. 



Computed 

 (photographic) 

 magnitude. 



Photometric 

 magnitude 

 U.N.O. 



Difference 

 C - O 

 in mag. 



No. 8 



35 



40. . . , 

 22 



lo'-Ol 

 4 *75 

 9-89 



11 -65 



7-27 

 9-43 

 7 31 

 6-70 



7-36 

 9-67 

 7-17 

 6-80 



-0-09 

 -0 24 

 + 014 



-o-io 



Table II. — Exposure 30 minutes. 



Star's 

 designation. 



Measured 

 diameter. 



Computed 

 (photographic) 

 magnitude. 



Photometric 

 magnitude 

 U.N.O. 



Difference 

 C - O 

 in mag. 



No. 8 



35 



40 



22 



14?4t 

 8-68 



15- 11 



16- 61 



7-44 

 9-51 

 7'22 

 6-77 



7 36 

 9-67 

 7-17 

 6-80 



+ 0-08 

 -0-16 

 + 0-05 

 -0-03 



Table III. — Exposure 60 minutes. 



Star's 

 designation. 



Measured 

 diameter. 



Computed 

 (photographic) 

 magnitude. 



Photometric 

 magnitude 

 U.N.O. 



Difference 

 C - O 

 in mag. 



No. 8 



35 



40 



22 



// 



15- 97 

 10-45 



16- 64 

 17 28 



7 33 

 9-42 

 711 

 6-91 



7'36 

 9-67 

 7-17 

 6-80 



-0-03 

 -0-25 

 -0-06 

 + 0-11 



