D. Kirkwood on certain Harmonies of the Solar System. 3 
forces; their tendency being to produce a rotation in a direction 
contrary to that of the orbital motion. hen the planetary 
mass, however, had gained considerable magnitude, the solar 
attraction would produce a tidal elevation on the hemisphere to- 
ward the sun. The gravitating force of this protuberant matter 
would maintain the greatest axis, during an indefinite period, in 
the direction of the central body; thus causing an equality be- 
: tween the angular velocities of rotation and orbital revolution, 
pe as is now found to obtain in the case of the secondary 
anets. 
Let us now consider the consequences of further condensation. 
Let S be the center of the solar mass; 
AC = D = the diameter of a planet’s sphere of attraction ; 
and ac=the diameter of the vaporiform planet at the close 
of the epoch of equality between the angular veloc- 
ities of the rotary and essive motions, 
It is obvious that the orbital velocity of a particle at ¢ must 
be greater than that of the center of the mass, while that of a 
 parti¢le at a must be less. Any further contraction of the sphe- 
- roid must tend therefore, to accelerate the rotation in the direction 
: 
: 
} 
4 
; 
a 
