AND ITS INHABITANTS 5 



sun, and as all the planets and planetoids are attendant upon 

 the sun, they form a common system, the solar system. The 

 facts regarding their size, their distance from the sun, and the 

 inclination and position of the planes of their orbits with 

 respect to the orbit of the earth are tabulated as follows: 



PRINCIPAL ELEMENTS OF THE SOLAR SYSTEM 



^ Inclination of sun's equator to earth's orbit. 

 2 Mean distance of moon from earth. 



Notable Planetary Relations. That the orderly nature of 

 this system implies some mode of evolution was seen by the 

 framers of the nebular hypothesis. The more notable of 

 these relations, following the summary by Young, are : 



1. The orbits are all nearly circular. 



2. They are nearly in one plane (excepting the cases of 

 some of the little planetoids). 



3. The revolution of all is in the same direction. 



4. There is a curiously regular progression of distances 

 from the sun (expressed by Bode's law, which, however, breaks 

 down at Neptune) . See foregoing table. 



