10 KNUT LUNDMARK, GLOBULAR CLUSTERS AND SPIRAL NEBULiE. 



Any considerable importance will scarcely be attached to this determination, 

 but it will nevertheless be permitted, in Joy's value for \i to see an upper limit for 

 the total proper motion of the cluster. 



M 92. N. G. C. 6341. At a comparison between SchultzV 82 micrometrical 

 measurements and his ovvn photographic ones, Bohlin 22 thought to hav T e found remar- 

 kable proper motions in this group. Micrometric and photographic measures per- 

 formed by Barnard 13-15 have, however, shown, that the differences found by Bohlin 

 cannot be due to proper motion, but are probably to ascribe to Schultz's incomplete 

 instrumental resources. Barnard finds only tvvo stars, for which the proper motion 

 amounts to a considerable value: 



0",083 225°,3I 



^r. (photographic measures) 



085 222,0) 



0,065 181,4 visual » 



Tlie total displacement of the cluster certainly amounts to a far lower value 

 than the proper motions of these stars, which perhaps do not belong to the cluster, 

 but probably are only projected against it. 



(o Centauri. N. G. C. 104. In recent years the stereocomparator has got an 

 important use in the searching for and measuring of the proper motion of the stars. 

 Innes 94 has shown that particularly good results can be obtained if the stereocom- 

 parator with the blink-arrangement is used. He has together with Voute measured 

 proper motions in w Centauri and finds, out of the 2000 stars on their plates be- 

 longing to the cluster, only 30 having a proper motion of l".o — 1",5 during 23 years. 

 |x = 0",05 must consequently be the upper limit for the individual motions within the 

 group. Innes has never stated that these stars are members of the group, and it is 

 probable that they do not belong to the cluster, but are perhaps only situated in 

 front of it. The individual motions within the system will consequently be diminu- 

 tive. Now the possibility remains that the cluster has a motion in common with 

 the background of the surrounding faint stars; against this supposition, however, 

 speaks the fact that the proper motions found by Innes agree well with the proper 

 motions, which for part of the stars in question have been determined out of the 

 Cape meridian observations. As these latter proper motions are to be considered, 

 in the case in question, as absolute, it is evidently probable that the proper motions 

 found by Innes are also absolute, and that, consequently, the background and the 

 cluster cannot have any common systematic motion. Even an amount of 0",oi is 

 probably altogether too high as a hypothetical upper-limit value for the total pro- 

 per motion. 



M 11. N. G. C. 6705. Photographically measured in 1896 by Stratonoff 219 , 

 micrometrically by Lamont 110 in 1838—39, and by Helmert 76 in 1869—70. The slight 

 systematic differences that remain between Stratonoff's and Lamont's and Helmert's 

 measurements, and of which a total displacement of the group might possibly form 

 part (page 132), show that the total proper motion of the group must be very small. 



