180 
ASTRONOMY: J. C. DUNCAN 
Proc. N. A. S. 
The resulting displacements of the nebulous points during the IIV2 year 
interval are as follows: 
Point 
A a 
A 5 
Point 
A a 
A 5 
1 
+0.22 
+0.70 
7 
-0.22 
+0.11 
2 
+0.43 
+1.24 
8 
+0.32 
-1.56 
3 
-1.24 
+2.05 
9 
+ 1.78 
-1.78 
4 
-1.67 
+ 1.24 
10 
+2.05 
-0.27 
5 
—1.12 
+ 1.59 
11 
+ 1.78 
+0.70 
6 
-2.16 
+ 1.19 
12 
+1.02 
-0.05 
The probable error of a measurement of a comparison star is ±0.23 
in right ascension and ±0.25 in declination. The points measured and 
the observed motions are shown in Plate I, in which the lines represent 
the displacements that would take place in 500 years if the motion should 
continue at the rate indicated by the measures. The illustration shows 
at a glance the random distribution of the motions of the stars and the 
systematic character of those of the nebulous points. The mean dis- 
placements, projected upon radii drawn from the estimated center of the 
nebula are: 
For the comparison stars, — 0 . 06 
For the nebulous points, +1.54 
The large positive value for the nebulous points clearly indicates an 
outward motion, but it would be premature to suppose that this result 
necessarily applies to the nebula as a whole. There is some indication of 
a rotation in the counter-clockwise direction, but this can hardly be re- 
garded as trustworthy. 
It may be readily shown that, for a displacement of 2" in the interval 
between the two plates, the number representing the velocity in kilo- 
meters per second would be about one-fourth the number of light-years 
in the distance of the nebula from the solar system; for example, if the 
velocity were 25km./sec. the distance would be 100 light-years. Thus 
it is necessary to assume neither an extraordinary distance nor an ex- 
traordinary velocity in the nebular particles in order to believe that the 
observed motions are real. 
1 Harvard Observatory Bulletin, Boston, No. 743, 1921; Publications of the Astro- 
nomical Society of the Pacific, San Francisco, 33, 1921 (79-84). 
