162 SEE— DYNAMICAL THEORY [April 19, 



this points to the expulsion of dust from the stars of the !\Iilky Way, 

 and its collection about the region of the formation in such manner 

 as to give essential symmetry in the final arrangement of the cluster, 

 which doubtless has some motion of rotation, and originally a tend- 

 ency to spiral movement. 



5. The stars and smaller masses are captured by the mutual action 

 of the other members of the cluster, and worked down towards the 

 center of the mass. This gives a central density in excess of that 

 appropriate to a sphere of monatomic gas in convective equilibrium 

 (^. //., 4053, and .^. A^, 4104). 



6. The density of the clusters is greater on the outer border than 

 in a globe of monatomic gas, which shows that stars are still collect- 

 ing from the surrounding regions of space. The starless aspect of 

 the remoter regions about clusters is an effect of the ravages of time, 

 as correctly inferred by Herschel in the course of his penetrating 

 sweeps of the starry heavens. 



7. And just as clusters under the mutual gravitation of the com- 

 ponent stars contract their dimensions, with time, chiefly owing to 

 the growth of the central masses, so also do other systems, whether 

 the mass-distribution be single, giving a system made up of a sun 

 and planets, or double, triple and multiple, giving binary, triple or 

 multiple stars, or sidereal systems of still higher order. The tend- 

 ency everywhere is from a wider to a narrower distribution of the 

 large bodies ; while the only throwing off that ever occurs is of par- 

 ticles driven away from the stars by the action of repulsive forces. 



8. The orbits of the stellar and planetary systems are decreased 

 by the growth of the central masses and rounded up by the action 

 of the nebular resisting medium. And in like manner all clusters 

 tend to assume spherical or globular figures, so as to justify the ex- 

 pression of Plato, that the Deity always geometrizes; or Newton's 

 remark that the agency operating in the construction of the solar 

 system was " very well skilled in mechanics and geometry." 



9. Newton required the intervention of the Deity to give the 

 planets revolving motion in their orbits, because in the absence of 

 repulsive forces he could not account for the dispersion of the matter, 

 so as to produce the tangential motions actually observed. By means 



