1910.] ABOUT THE FIXED STARS. 227 



This proof that the planets never were any part of the sun, but 

 have come to it from great distance, is accompanied by an argument 

 based on dynamical principles showing that the same thing will 

 happen for any other star developing in a nebula ; and it is, there- 

 fore, certain that the other stars have planetary systems revolving 

 about them. The argument is based on the recognized laws of 

 dynamics and verified by the known history of the solar system, 

 and therefore seems to be entirely satisfactory. 



The difficulty and uncertainty, as to the existence of planets 

 about the fixed stars generally, appears, therefore, to be overcome ; 

 and we conclude that the discovery of the true process of formation 

 of our system enables us to affirm with confidence that nearly all 

 the fixed stars have systems of planets revolving about them. Here 

 is the foundation of the new line of argument. 



1. The observed motions of the double stars show that the law 

 of gravitation is universal, and that the same law of attraction that 

 holds true for the bodies revolving about the sun also regulates the 

 motions of the remotest stars. 



2. This indicates that the forces are central, and that the same 

 laws of areas and of motion hold there as in the solar system. 

 Similar effects imply similar causes, and hence the double stars 

 have been set revolving by projective forces and other causes 

 analogous to those which set the planets in motion about the sun. 



3. These movements resulted from nebular vortices, formed 

 by the settlement and winding up of streams of nebulosity which 

 did not pass through the center, but circled about it. 



4. Such is the phenomenon shown in the spiral nebulae, which 

 are proved to exhibit the usual process in the development of cos- 

 mical systems. Nebulae are formed from cosmical dust expelled 

 from the stars, and it cannot fall to a center to produce a central 

 sun without giving rise to a whirling vortex about that center, 

 since but few of the streams will converge in a point. 



5. Planets form in the streams which make up a spiral nebula, 

 and in some cases they unite to form a double star, the system thus 

 developing into a double sun ; but in the more typical case the 

 planets are too small to be seen and the stars appear to be single. 



