ASTRONOMY: C. D. PERRINE 
293 
Region Apex Antapex 22^-2^ lOh-U^ 10^-14^1 10h-14h2 
Magnitude 4.4 4.0 4.3 3.7 4.3 3.7 
Vzinkm 7.8 6.2 6.8 5.9 7.1 6.0 
Proper Motion 0'r014 0:'013 0'f020 0:'043 0^^038 0':040 
No. of stars 21 44 18 27 20 26 
1 Omitting all stars brighter than 3''0 to make average magnitudes comparable with region 
at 22^-2^. 
2 Omitting the only apparently abnormal value oi ix = 0''119. 
A cursory examination of the right ascensions of Boss' Preliminary 
General Catalogue reveals a consistently smaller number of very small 
proper motions in the region 10^ to 14^ than in the region 22^ to 2^. A 
preliminary examination of the A stars shows a similar (but smaller) 
effect if we omit the stars having proper motions of 0" . 2 and over. 
At the time of finding asymmetry in these proper motions the deter- 
mination by Charlier of the motion of the node of the invariable plane of 
the solar system on the plane of the Milky Way was unknown to me. 
The value for the motion derived by CharHer and the preliminary value 
obtained by me from the B stars are as follows : 
Charlier (Boss P. G. C.) + 0^0035 per year, 
Perrine (class B) +0.012 per year. 
If the observed phenomenon is in reaUty a relative motion of the in- 
variable plane with respect to the Milky Way as a whole the angular 
motion as derived from different classes of stars, but especially from stars 
at widely different distances, should be exactly the same. The above 
discordances in the values throw doubt on the constancy of that angle. 
Preliminary solutions for the apex and velocity of solar motion from 
northern and southern stars separately of class B and of 110 stars 
brighter than 3.0 magnitude of all spectral classes give systematically 
different results. The solar velocities derived in this way have a par- 
ticular bearing on the above question and are given below. 
Northern Stars Southern Stars 
km. km. 
Class B, 3.0 and fainter -17.0 -24.8 
2 . 9 and brighter, all spectral classes —14.4 — 24 . 5 
If there is no motion of rotation the values of the solar velocity de- 
rived from these different regions should be the same except for the ef- 
fects of accidental variations whether the invariable plane is in motion 
or not. If however, the stellar system is rotating in a retrograde direc- 
tion about the poles of the Milky Way, exactly such differences as the 
above should result. 
It seems highly probable that the invariable plane may also be in 
motion. 
