498 
ASTRONOMY: CAMPBELL AND MOORE 
For an assumed apex of the sun's way at Right Ascension 270° and 
Declination +30°, the 73 planetaries give a solar velocity of 2.01 
km./sec, while the 7 extended nebulae give 20.7 km. /sec. These 
values are in remarkable accordance with that derived from 225 Class 
B stars, namely, 20.2 km./sec. 
When the results for the 73 planetary nebulae are examined for the 
existence of preferential motions, in accordance with Kapteyn's two star- 
stream hypothesis, it is found that they show a marked preference for 
motions making small angles with the line joining Kapteyn's two ver- 
tices. A similar indication is shown when the velocities of these nebulae 
are grouped with reference to their distances from the central line of the 
Milky Way, a conclusion which is entitled to less weight, since only 10 
of these objects are situated more than 20° from the galactic plane. 
The fact that the gaseous nebulae have motions which are character- 
istic of the stars, as shown by the value of the solar motion derived 
from them, and by their exhibiting the phenomena of star streaming, 
taken together with their strong concentration in the Milky Way, affords 
a reliable basis for the view, frequently expressed, that these nebulae 
are members of our stellar system. 
Since the announcement^ by Dr. Wilson of the high velocities of 
5 nebulae in the Magellanic Clouds, 7 more of these objects have been 
observed. The only known nebula in the Lesser Cloud has a velocity 
of recession of 149 km./sec, while 11 nebulae observed in the Greater 
Cloud have velocities of recession ranging between 4-237 and -f 287 
km./sec. 
In as much as gaseous nebulae are unknown in the surrounding 
regions of the sky, it is a fair assumption that all of these bright-line 
objects are within the structure of the two Clouds. It is therefore 
probable that the velocity of the Greater Cloud with reference to the 
stellar system is approximately the average velocity of the 11 nebulae 
observed within it, or 262 km./sec. recession. The observed velocity 
for only one object in the Lesser Cloud is hardly sufhcient to justify 
an analogous h3rpo thesis for it. However, the similarity in the appear- 
ance of the two clouds and their proximity to each other lead to the 
suspicion that a more or less intimate relationship may exist between 
them. Furthermore, the high galactic latitudes of these objects, coupled 
with their high velocities with reference to the centroid of stars, lends 
some support to the hypothesis that the Magellanic Clouds are isolated 
cosmic units, systems which have no apparent connection with our 
own stellar system. 
'These Proceedings, 1, 8 (1915). 
^Ibid., 1, 183 (1915). 
