DEVELOPMENTS IN ASTRONOMY PLASKETT. 267 



were determined by spectrographs at Lick and Santiago, 40 were 

 obtained from other observations and 13 were of nebulae visually 

 observed by Keeler. The position of the apex, or point toward 

 which the sun is moving, is somewhere, about 7° south of that obtained 

 from the proper motions of the stars (R. A. 272° ± 2.5°, Dec. 27.5° 

 ±3°), nearly 10° due south of Vega. 



Of the two determinations, the one obtained from a discussion 

 of the proper motions is of the greater weight, for two reasons — first, 

 the method is more suitable for determining direction; second, the 

 number of stars employed is considerably greater. 



On the other hand, the discussion of radial velocities gives us a 

 much more reliable value of the velocity of the solar system than 

 proper motions. The velocity from Campbell's discussion comes out 

 as 17.77 kilometers (11 miles per second), and this is undoubtedly 

 very near the truth. 



Many other interesting conclusions were reached by Campbell, but 

 time will not permit me to dwell on them, and we must consider 

 further the question of motion of the stars. 



It is evident that if a comparison of the motions of the stars shows the 

 sun to be moving toward Vega, then the apparent motions of the stars 

 themselves must, on the whole, be to a point on the celestial sphere 

 directly opposite. Such a motion of the stars, made up not of 

 motions all in the one direction, but of motions in all directions with a 

 preponderance in one direction, is called a drift of the stars; and there 

 is thus a drift of the stars due to the solar motion toward or having 

 as apex a point in the Southern Hemisphere nearly opposite Vega, 

 with a velocity of about 11 miles per second. 



About five years ago Kapteyn, from a careful examination and dis- 

 cussion of the proper motions of the Bradley stars, came to the con- 

 clusion that there is not one drift of stars, that due to the solar motion, 

 but two drifts, moving in different directions. Tins conclusion has 

 been confirmed by Eddington, Dyson, Hough, and Halm, and the latest 

 values by Eddington from the proper motions of Boss's Catalogue 

 place the apexes of these two drifts as follows: Drift I toward the 

 constellation Lepus between Canis Major and Orion, about 10° west 

 of Sirius (R. A. 90.8°, Dec- 14.6°; drift II toward the southern 

 constellation Pavo or away from the northern constellation Camel o- 

 pardalis (R. A. 287.8°, Dec. - 64.1°). He finds that drift I is moving 

 apparently nearly twice as fast as drift II and contains about 60 per 

 cent of the stars. 



When, however, allowance is made for the solar motion we find that 

 these two drifts are moving, one toward the constellation Orion about 

 8° northeast of a Orionis (Betelgeux), R. A. 94.2°, Dec. + 11.9°, and 

 the other in the opposite direction; exactly as if we were in the midst, 



