1904 - 5 .] Dr J. Halm on the Nebular Hypothesis. 557 
smaller particles around them. Now let us consider the effect of 
these mutual attractions. Ail the particles in front of the nucleus 
(counting in the direction of the rotation of the ring) are pulled 
towards the condensation by forces, the tangential components of 
which are acting against their orbital motions round the central 
star. It is evident that these particles must fall towards the sun ; 
they acquire radial velocities in the inward direction. Exactly 
the opposite course of events must happen with particles in the 
rear. Here the tangential pull is in the direction of orbital 
motion ; they must move from the sun, and hence acquire radial 
velocities in the outward direction. On the other hand, the 
attraction of the particles on the nucleus acting equally in all 
directions, the latter suffers no deflection from its original motion. 
Now it is easy to picture what will happen when the attracted 
particles coalesce with the nucleus. The conclusion is that 
neither the front nor the rear particles fall directly towards the 
centre of the condensation: all the front particles must show a 
tendency to swing round on the inner side, i.e. between nucleus 
and sun, and all the rear particles on the outer side. Hence the 
accreting meteors must impart a rotary motion to the condensing 
nucleus, and the direction of this rotation must necessarily he 
that of the ring itself. Here, then, we have the conditions of 
rotary motions actually existing in our system. 'Whereas Laplace 
explains planetary rotation by the difference of speed between 
the outer and inner parts of the ring, which he must therefore 
assume to rotate with uniform angular velocity, we find now 
that the detachment of a Laplaceian ring and its subsequent 
coalescence into a planet is not necessarily required to account 
for the rotary motions of the planets. 
The next point I desire to illustrate may be inferred from the 
following consideration. Let us imagine two bodies of equal 
masses to revolve in the same circle round the sun. Suppose, also, 
that the distance between the two bodies is sufficiently great to 
permit us to neglect their mutual attractions. Obviously the 
time of their revolution will also be exactly the same, and hence 
their distance from each other will remain unaltered. But let us 
assume their masses to be unequal. The period of revolution of 
the heavier body being shorter than that of the lighter body, the 
