DEVELOPMENTS IN ASTRONOMY—PLASKETT. 267 
were determined by spectrographs at Lick and Santiago, 40 were 
obtained from other observations and 13 were of nebule 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. 
Itis 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. This 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 Camelo- 
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 
