WEIGHING THE WORLDS 



weighed in the facile manner just indicated. In at- 

 tempting to compute their mass, it is necessary to 

 take into account their observed perturbing effects 

 on the orbits of comets that chance to pass near 

 them from time to time, and at best the results ob- 

 tained are somewhat less trustworthy than those 

 secured in the case of the other planets. Large 

 numbers of observations, however, have given fairly 

 concurrent results, and it is computed that Venus 

 weighs about %o and little Mercury about %s as 

 much as the earth. The density of Venus is 4.89 and 

 that of Mercury 3.70. These inferior planets are, 

 therefore, not very dissimilar to the earth in point 

 of solidarity. 



ARE THE PLANETS INHABITED? 



Time out of mind the question whether there are 

 human inhabitants on the planets has been matter 

 of interest and controversy. The question has been 

 argued pro and con from many standpoints, includ- 

 ing the theological, but it can not fairly be said to 

 be settled even in our own day. In a recent book 

 Professor E. Walter Maunder, Superintendent of the 

 Solar Department of the Royal Observatory at 

 Greenwich, England, discussed the question of the 

 habitability of the various planets, and gave what 

 may be considered a fair presentation of the attitude 

 of the generality of astronomers toward this inter- 

 esting subject. 



As to all but two of the planets, the question may 

 be answered negatively with entire assurance. The 

 great gutlying planets Jupiter, Saturn, Uranus, and 



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