FEBRUARY 9, 1912] 
kilometers per second. 61 Cygni appears to be a 
member of this group (A.J. 629). 
Before seeking a systematic representation in 
direction and amount of the star motions generally 
the speaker had wished first to follow up the indi- 
cations which had already appeared to the effect 
that the stars of differing spectral types are 
moving with differimg mean velocities. Frost, 
eight years ago, had offered the earliest evidence 
that the Helium, or Orion, stars are moving slowly 
in comparison with those of older types. Quite 
recently he and Kapteyn and also Campbell added 
some preliminary evidence to the discussion of 
this question. In the winter of 1910-11 the de- 
partment determined to take up this subject com- 
prehensively by employing the cross-motion ele- 
ment of the proper motions. The results of this 
research on acceleration of stellar motion were 
published in the Astronomical Journal, Nos. 623 
and 624. These results are given in the following 
table under the column designated ‘‘mean cross 
motions.’’? For comparison, Campbell’s results 
from mean radial motions are given in the next 
column. ‘They were obtained from entirely dif- 
ferent sources, independently and almost simul- 
taneously. The letters in the first column, in 
which B is supposed to stand for the youngest 
spectral type (Helium), and M for the oldest 
considered in this investigation, are designations 
adopted from the Harvard classification (H. C. O., 
Vol. L.). 
Mean Mean 
Type Cross Motions Radial Motions 
B Ga 6.2 
A 10.2 10.5 
F 16.2 14.4 
G 18.6 15.9 
K 15.1 16.8 
mM 17.1 17.1 
The cross motions were originally expressed as 
a fractional part of the centennial motion of the 
sun. Both series, in good agreement, express the 
fact that the motion of a star accelerates up to 
about the time the spectrum develops into type F 
or G, after which it seems to gain no increase of 
velocity. 
Seven years ago Professor Kapteyn, at the 
Scientifie Congress of the St. Louis Exposition, 
introduced his now well-known hypothesis that the 
visible universe consists of two great intermingling 
streams moving in opposite directions. The direc- 
tion of one he called the ‘‘ vertex,’’ which he fixed 
at R.A. 6"4™, Decl. + 13°. Quite recently Edding- 
SCIENCE 
221 
ton, of the Greenwich Observatory, with the same 
hypothesis, and using the proper motions of the 
‘‘Preliminary General Catalogue,’’ found for this 
vertex: R.A. 616™, Decl. + 12°. 
In 1907 Schwarzschild advanced the hypothesis. 
that a systematic arrangement of the proper mo- 
tions leads to an ellipsoidal arrangement of dis- 
tribution and he endeavored to show that the 
proper motions of Groombridge’s Catalogue are 
as well represented as they are by the hypothesis. 
of two streams. 
By a method entirely different from that em- 
ployed by either of the two investigators, the 
department found nearly a year ago that when its 
proper motions were compared in a manner to 
bring out this systematic arrangement, it was 
seen that if all the actual motions of the stars in 
any considerable area of sky were brought to a 
common origin (freed from their solar parallactie 
motions) the figures so constructed would have an 
elliptic outline, which turned out to be different 
presentations of an ellipsoidal figure of which, if 
the major axis be taken as 7, the two minor axes 
would be 4. The major axis of all the figures 
points very nearly toward the vertex of Kapteyn; 
this point was found to be in R.A. 6715" and 
Decl. + 7°. Moreover, these ellipsoids have well- 
marked nuclei composed chiefly of stars of types 
Band A. This fact would require a third stream 
to complete the ‘‘two-stream’’ hypothesis, as some. 
of the supporters of the latter have already per- 
ceived. 
The speaker presented considerations in support 
of his belief that this ellipsoidal arrangement of 
the star-motions in space would be reduced to a 
simple and natural explanation, if we suppose that 
the stars had been originally formed in nebulas 
and repelled from the regions of their formation 
_ with a tendency to be impelled by some kind of 
polarity 50 to 75 per cent. faster in the direction 
of the major axis of the ellipsoid than in a direc- 
tion at right angles to that. This hypothesis also 
fits in well with the undoubted phenomenon of’ 
acceleration of a star’s motion with age. 
The section elected President E. O. Lovett mem-- 
ber of the council, Professor F. B. Littell member 
of the sectional committee, and Dean H. T. Eddy 
member of the general committee. On recom-- 
mendation of the sectional committee Professor E.. 
B. Van Vleck, University of Wisconsin, was; 
elected chairman of the section by the generali 
committee. G. A. MILLER, 
Secretary of Section A 
UNIVERSITY OF ILLINOIS 
