148 
ASTRONOMY: S. B. NICHOLSON 
the satellite's motion is sufficient to give a fair idea of the principal 
characteristics of the orbit. These are best exhibited by the accom- 
panying diagram which shows the orbit projected on a plane (incHned 
to the ecliptic at an angle of 24°) from which it does not deviate greatly 
during 1914 and 1915. At the end of 1916, however, the satellite as seen 
from Jupiter was about 4° from this plane. The dotted line in the dia- 
gram shows the intersection of the projection plane with the plane of the 
SCALE IN ASTRONOMICAL UNITS 
ORBITS OF JUPITER'S EIGHTH AND NINTH SATELLITES 
«ecliptic. The feathered arrow points in the direction of the vernal equi- 
nox. Since the motion of the satellite is retrograde, the corresponding 
values are for i and Q. are 156° and 310°, respectively. For comparison, 
the orbit of the Eighth Satellite from the investigation by A. C. D. Crom- 
melin^is also shown, projected on the same plane as the orbit of the Ninth 
Satellite. The angle between the two orbit planes is about 10°. The 
points where the satellites pass above and below the plane of projection 
are designated by the letter P. The small circles indicate the positions of 
