ASTRONOMY. 12i) 



t^3^ Dr. Elkiii has taken in all the stars in the Dnrcliransterungdown 

 to 9.2 magnitude, which may reasonably be said to fall within tlie group, 

 and in so doing he has rejected one of the stars used by Bessel in his 

 celebrated work with the Konigsberg heliometer as too faint for accu- 

 rate measurement, but he has added seventeen stars to Bessel's list of 

 fifty-three, so that he has taken sixty-nine stars in all. Two practically 

 independent methods of measurement were adopted. The first plan 

 was to measure the distance of each star of the group from each one of 

 four reference stars situated so as to form a quadrilateral symmetrically 

 placed about the group; the position of each star thus depended on 

 measures of distance alone. The second plan was to measure the posi- 

 tion-angle and distance of each star from -q Tauri or Alcyone, the cen- 

 tral star of the group. The work on the quadrilateral plan was com- 

 menced in March, 1884, and lasted to December — the measures from r) 

 Tauri occupied the first three and last four months of 1885, the mean 

 epoch of the second triangulation falling about a year later than that 

 of the first. Dr. Elkin gives a brief description of the instrument with 

 his method of using it, and this is followed by a determination of the 

 instrumental constants and by the observations in detail. The defini- 

 tive results are then critically compared with Bessel's heliometer work 

 and with the filar micrometer measures of Wolf at Paris and Pritchard 

 at Oxford. The comparison with the Konigsberg observations shows 

 that for the six largest stars there is a striking community of mo- 

 tion, both in direction and in amount, and it is remarkable that this 

 general direction of drift is very similar to the reversed absolute motion 

 of Alcyone as given by Newcomb. Dr. Elkin thinks the coincidence is 

 sufficiently close for two of the stars at least, and possibly for the other 

 four, to warrant the conclusion that they are only optically members of 

 the group. Of the remaining twenty-six of the thirty-two stars show- 

 ing some displacement since 1840, the epoch of Bessel's catalogue, the 

 distribution of the direction of motion is by no means equable, six stars 

 only having an easterly- motion, while twenty move towards the west, 

 and here too there seems to be a tendency to community of drift in cer- 

 tain groups in the same part of the cluster. 



''The general character of the internal motions of the group appears 

 to be thus extremely minute. If for the six stars mentioned as with 

 more or less probability not belonging to the group this proves to be 

 the case, there are but five stars for which the displacement amounts to 

 over one second in forty-five years. The bright stars especially seem 

 to form an almost rigid system, as for only one is there really much evi- 

 dence of motion, and in this case (star h) the total amount is barely one 

 second per century. The hopes of obtaining any clew to the internal 

 mechanism of this cluster seem therefore not likely to be realized in an 

 immediate future." 



Professor Hall has measured with the L'O inch Washington refractor 

 the positions of sixty-three small stars in the groiij) relatively to the 

 U, Mis, 142 — -9 



