KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 60. NIO 8. 9 



7Tm=4,74^- (2) 



The sources at my disposal for a determination of the total proper motion of 

 globular clusters are, unfortunately, very insufficient, partly because it has not been 

 possible to perform any reliable measurements of positions of stars in these objects, 

 before the photographic measuring methods had been worked out and acknowledged, 

 partly because astronomers have as a rule been more interested in the relative mo- 

 tions in the globular clusters, and less devoted themselves to the determination of 

 the translational motion and even not always taken care that the measurements 

 may be connected with such surrounding står that can be regarded as not being 

 physical members of the group. 



For the following globular clusters there exist measures of the positions of the 

 individual stars in the duster. 



M 3. N. G. C. 5272. One of the most extensive measurements yet published 

 of the positions in a globular duster is the one performed by von Zeipel for M 3 251 . 

 Unfortunately there exist no earlier meaurements, and the epochal difference is 

 probably too small to justify a new measuring, but when the work is låter on to 

 be repeated, an important contribution to our knowledge of the translation and the 

 internal motions in this stellar system can be expected. 



M 13. N. G. C. 6205. Measured by Scheiner 176 , Ludendoeff 119 , H. C. 157 and 

 W. E. Plummer 168 . The measurements of the last author have not yet been com- 

 pletely published. A fevv small differences of systematic character seem to remain 

 between the different measurements. Thus Ludendorff finds a systematic diffe- 

 rence between Scheiner's declinations and his own of the form dd = — 0",o6AS, which 

 he is inclined to ascribe not to motion but only to a difference in scale-value. Lu- 

 dendorff^ and W. E. Plummer's discussion of the 4 series of measurements of 

 M 13 show, that also this globular cluster must be considered as having a very 

 slight lateral motion. 



M 37. N. G. C. 2099. Three series of measurements performed by Nord- 

 lund 134 , Giebeler 69 and Jo v" are in hand for this globular cluster. The comparison 

 made by Giebeler between his own measurements and those performed by Nord- 

 lund show a rather great difference in declination, evidently owing to a magni- 

 tude equation originating from a prolongation of Nordlund's photographic images. 

 Partly on this account, and partly as the epochal differences are comparatively 

 small, these measurements cannot be used for an estimate of the total proper mo- 

 tion of the cluster, which motion, however, judging from Giebeler's discussion, is 

 evidently very small. Thus Joy finds by his measurements, from a comparison 

 between plates taken with an interval of 11, os years, that the total proper motion 

 of the cluster, relatively to the reference stars, has the value: 



tx = 0",oo66 ; p = 46°,2. 



K. Sv. Vet. Akad. Hand]. Band 60. N:o 8. 2 



