WEIGHING THE WORLDS 



makes it difficult to confirm these observations, and 

 the question of the rotation period of the planet is 

 still an open one. On the solution of that question 

 will depend the answer to the other question as to 

 whether Venus may or may not be the abode of life. 



WEIGHING THE STARS 



It is a natural assumption, speaking from a terres- 

 trial standpoint, that some or many of the stars may 

 have planetary systems comparable to that of our 

 particular star, the sun. Much of this was tacitly 

 assumed in what was said in an earlier chapter about 

 the possible development of stellar systems out of 

 spiral nebulae. But it should be explained that the 

 existence of such minute planetary attendants as 

 those that make up the sun's family is a matter of 

 pure conjecture, subject neither to verification nor 

 refutation unless some far more powerful means of 

 investigation than those provided even by our largest 

 telescopes shall be developed. 



To understand this it is only necessary to recall 

 that computation shows that if the nearest star, 

 Alpha Centauri, had a planetary attendant similar to 

 the earth, its astronomers, even if provided with 

 telescopes equal to the great Mt. Wilson reflector, 

 would be unable to discover that our sun has any 

 attendants. The sun itself would appear as a small- 

 ish first magnitude star, and the very best that could 

 be hoped would be that the giant Jupiter would be re- 

 corded on a photographic plate as a star of less than 

 the twenty-first magnitude at a seeming distance of 

 only five seconds from the sun. Yet Alpha Cen- 



9 1 



