THE PLANETS, ARE THEY INHABITED ? 



The meaning of this is, that if 338| masses of matter like the 

 earth were placed in one scale of a colossal balance, and the 

 single globe of Jupiter in the other, the beam would be exactly 

 equipoised. 



24. A very curious inference follows from this. It appears 

 from what has been shown, that the volume or bulk of 

 Jupiter is 1,330 times greater than that of the earth, so that it 

 would require 1,330 globes like the earth to be moulded into a 

 single globe to make such a globe as Jupiter, while 338^ such 

 globes would be sufficient to make a globe as heavy as Jupiter. It 

 is evident, therefore, that bulk for bulk, the matter composing 

 Jupiter, is lighter than the matter composing the earth, in the 

 ratio of 338| to 1,330, or what is the same, of 4 to 1. 



It has been proved that the earth is 5^ times the weight of 

 an equal globe composed of water. It follows therefore that 

 Jupiter is heavier than an equal globe of water in the far less 

 proportion of 54? to 4, or 1| to 1. 



It was shown that if Jupiter were composed of matter like 

 the earth, the weight of bodies upon his surface would be 

 11 times greater than upon the earth. But since it appears that 

 it is composed of matter 4 times lighter than that of the earth, 

 it will follow that the weight of bodies upon its surface will be 

 4 times less than the weight previously computed, and that it 

 will therefore be only 2f greater than upon the earth. 



Thus it seems that owing to the comparative lightness of the 

 matter composing this great globe, the attraction which it exerts 

 upon bodies placed upon its surface, though greater than upon the 

 earth, does not exceed terrestrial gravity in a proportion which 

 requires the admission of any difference of organisation of the 

 inhabitants, exceeding what may be imagined without removing 

 Jupiter from the general analogy of the earth. 



25. The other three planets of the exterior group, being 

 attended by satellites, can be weighed against the earth by com- 

 paring, as in the case of Jupiter, the motions of their moons with 

 that of the earth's moon, and after making due allowance for the 

 difference of distance, the attractions which they would severally 

 exert, compared with that exerted by the earth, becomes the 

 expression of the relative quantities of gravitating matter com- 

 pared with that of the earth. 



It is thus found that the weight of Saturn is 101 times, that of 

 Uranus 14, and that of Neptune 19 times the weight of the earth. 



It appears, therefore, that while the bulk of Saturn is 857 

 times greater than that of the earth, its weight is only 101 times 

 greater. It is therefore lighter, bulk for bulk, than the earth, 

 in the proportion of 101 to 857, or 1 to 8J. 

 30 



