22 
ASTRONOMY: F. G. PEASE 
During the exposure the slit crossed the nucleus and coincided with the 
major axis which lies in position angle 40°. The slit-width was 0.025 mm., and 
the spectrogram was traversed longitudinally by comparison spectra at inter- 
vals of 1 mm. (see fig. 1). 
The results of measures by Mr. Adams and Miss Burwell are given in table 1. 
The correction for the earth's motion is slight and has been neglected. To re- 
duce the accidental errors and equalize the weights somewhat, results for 
adjacent sections of spectra in the outer regions have been combined. The 
values for extreme sections, which are very uncertain, are given separately and 
appear in parentheses in the table. The values of the distance from the nu- 
cleus have been corrected for magnification by the spectrograph. The tabu- 
lated radial velocities must be corrected for the inclination of the nebula to 
the line of sight. Assuming the nebula to be circular, the ratio of the major 
and minor axes of its apparent elliptical outline, which is 4 to 1, is a measure 
of the inclination. We thus find approximately 14° as the inclination, and 
the velocities must accordingly be multiplied by 1.03 to reduce them to the 
plane of the nebula. 
The mean velocities of table 1 are shown in figure 2, the ordinates being 
kilometers per second and the abscissae seconds of arc. The velocity curve 
y = -0.48 x -316 
was determined graphically. From this equation we find: 
1. The radial velocity of the nebula is —316 km., a value in good agreement 
with the earlier measures: 
km. 
Pease and Adams 1 . — 329 
Pease and Adams 2 —297 
Slipher 3 -300 
Wolf 3 -350 
Wright 3 -304 
2. The linear velocity of rotation at a point 2 minutes of arc from the 
nucleus is 58 per second. 
3. Within the distance measured and the limits of accuracy of the measures 
the change of rotational velocity with distance seems to be linear, although 
there may be variations at individual points in the nebula. 
4. Whether the motion of the nebula is inward or outward along the arms 
of the spiral depends upon the inclination of the nebula. 
From a spectrogram of eighty-four hours exposure made at intervals dur- 
ing August, September, and October, 1916, with the slit placed on the minor 
axis of the nebula, Mr. Adams obtains the results shown in table 2. 
These velocities, which are nearly constant, are also shown in figure 2 
the velocity curve obtained for points along the major axis, and greatly with 
