A GIANT PLANET. 87 



is one of a family of orbs, nearly equal in dignity and 

 importance, and comprising the Earth and Venus, 

 Mars and Mercury, among its members. This idea 

 still prevails, because in our books on astronomy we 

 commonly see a set of concentric circles, at regularly 

 increasing distances, assigned as the paths of the 

 several planets of the solar system. And besides, 

 there yet remains in the modern teaching of astronomy 

 a perceptible trace of the ancient astronomical systems, 

 in which Saturn and Jupiter, Mars, Venus, and 

 Mercury, played parts of equal importance. 



Let it be carefully remembered, then, that the four 

 planets which circle nearest to the sun, the family of 

 which our earth is a member, differ in all their 

 characteristics from the outer family (also consisting 

 of four planets) to which Jupiter belongs. The whole 

 of the inner family the whole of the space within 

 which its members travel could be placed between 

 the paths of Jupiter and his next neighbour Saturn, 

 with a clear space many millions of miles wide on 

 either side. The actual area between the paths of 

 Jupiter and Saturn exceeds nearly thirty times the 

 whole area within which the four lesser planets pursue 

 their paths. And when we consider the dimensions of 

 the four inner planets we find a like disproportion. 

 Four circles representing these orbs can be enclosed 

 within a circle representing Uranus, the smallest of 

 the four outer planets ; yet even this circumstance does 

 not adequately represent the enormous disparity 

 between the two families of planets : for, in fact, the 



