1116 



-^ = 2.55 .T==0".0005 



-4l2.9 



^^ = 2.16 jr = 0".0007 



^13.4 



From 6 detenninatioiis we (liid as tlie mean : 

 .T = 0".00055 zb 0.00003 (p. e.) 



According to Shapley the average photogr. magnitude of the 

 variable stars is 15.5 and 5 log n =z — 16.3, so that we get as the 

 mean absolute magnitude for these stars .1/ = J 5'" .5 — 11'" .3 = 4"' .2. 



The average period is Ü'^.54, so that, according to Hertzsprung, 

 the absolute magnitude J/=rO"'.0 (visual). If, imitating Hertzsprung, 

 we assume the colour-index of the variable stars in the cluster to 

 be H-l"'.5, we shall find in this way for the parallax .-t==0".0001 5. 



h and / Persei. 



h Persei, ^V. G. C\ 869, «,,.„ r= 2'' 12'" .0, rf,„. = + 56°41', 

 b = — S°, / = — 103° ; class : D 2. 



^ Persei, A^. G. C. 884, .^„. =: 2'' 15'" .4, rf., „. = -f 56°39', 

 6 = — 3°, /=103°; class: D 2. 



0. A. L. PiHL. The stellar cluster / Persei micrometrically 

 surveyed, Christiania, 1891. 



This catalogue contains the places and magnitudes of 236 stars. 

 The magnitudes have been determined visually with great exactness 

 in accordance with Vogel's observations with a Zöllner Photometer. 



K. ScHWARZscHiLD. Beitrage zur photographischen Photometric der 

 Gestirne, Publ. der V. Kuffner'schen Sternwarte in Wien, Bd. V, 

 C 1—138. 1900. 



This publication contains i. a. the photographic magnitudes of 

 111 stars in x Persei and 91 stars in h Persei. They have been 

 found by taking extrafocal photos and by comparison with observa- 

 tions of the Pleiades. 



A. VAN Maanen. The Proper Motions of 1418 stai-s in and near 

 the clusters h and x Persei, Diss. Utrecht 191 1, Recherches astrono- 

 miques de TObservatoire d'Utrecht V. 



Four plates of Kostinskv and two of Donner have been measured. 

 Of 1410 stars the diameter has been measured. In order to find 

 standard magnitudes the B.D. magnitude for bright stars, corrected 

 in accordance with Annals Harvard Observ. Vol. 54, was used; 

 for stars with less brightness the magnitude was determined from 

 counts of stars with the aid of Publ. Gron. N". 18 and from 

 estimations by Nijland. 



