A GIANT PLANET. 287 



cause 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 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 neighbor 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 cii'cle representing Uranus, the smallest 

 of the four outer planets ; yet even this circumstance does not ade- 

 quately represent the enormous disparity between the two families of 

 planets ; for, in fact, the volume of Uranus exceeds the combined vol- 

 ume of all the inner planets upward of thirty times. We might ad- 

 duce many other illustrations of the complete dissimilarity between 

 the inner and outer families of planets ; but what has been already 

 stated will suffice for our present purpose. It will be evident that, in 

 considering the members of one or other family, we must be prepared 

 to meet with relations which differ not merely in degree, but in kind. 

 We may thus, at the outset, dismiss from our thoughts the idea that 

 the planet Jupiter is necessarily to be regarded as an inhabited world 

 merely because the only planet we are actually acquainted with is 

 inhabited. The latter circumstance may be an excellent reason for 

 regarding Mars or Venus as the abode of life ; but the analogy can no 

 more be extended to Jupiter than to the fixed stars, which certainly 

 are not inhabited worlds. We must, in fact, consider the physical 

 habitudes of Jupiter independently of all conceptions based upon terres- 

 trial analogies. Studied thus, he will be found, as we conceive, to hold 

 a position in the scheme of creation differing considerably from that 

 which has been assigned to him, until of late, in treatises on astronomy. 



It is necessaiy briefly to state the dimensions, mass, and general 

 characteristics of the planet, before proceeding to discuss its probable 

 physical condition. 



Jupiter has a diameter exceeding the earth's rather more than ten 

 times, and a volume exceeding hers 1,230 times. It is not far from 

 the truth to say that Jupiter's dimensions exceed the earth's in very 

 nearly the same degree that those of the sun exceed Jupiter's. But his 

 mass, though gigantic compared with the earth's, does not altogether 



