THE PLANETS, ARE THEY INHABITED ? 



on the quantity of matter in the globe, and on the distance of the 

 body from its centre, which distance will be the radius or semi- 

 diameter of the globe. The greater the quantity of matter 

 composing the globe, the greater will be the attraction which 

 it will exert upon a body at a given distance from its centre, 

 But this attraction will be less as that distance is increased, in- 

 the proportion of the square of the distance. 



23. Now let us apply these principles to the major planets ; 

 to Jupiter for example. 



The volume of Jupiter, as we have stated, is 1,330 times that 

 of the earth. If it be composed of materials similar to those 

 which compose the earth, its mass or quantity of matter will be 

 1,330 times greater than that of the earth, and it would conse- 

 quently exert an attraction 1,330 times greater than terrestrial 

 gravity upon a body at the same distance from its centre. 



Now, the body of an average man placed on the surface of 

 the earth, and therefore at a distance from its centre equal to 

 half its diameter, is attracted towards that centre with a force 

 of 150 Ibs. The same body placed at the same distance from the 

 centre of Jupiter would, on the above supposition, be attracted 

 with a force of 1,330 times 150 Ibs. But bodies placed on the 

 surface of Jupiter are at a distance from its centre eleven times 

 greater than the semi-diameter of the earth, because the semi- 

 diameter of Jupiter is greater than that of the earth in the 

 proportion of 11 to 1 ; and, consequently, if the body of the man 

 were placed on the surface of Jupiter, it would be attracted with 

 a less force in the ratio ot the square of 11, that is of 121 to 1, 

 The account would therefore stand thus : 



Ibs. 

 Weight of a man on the surface of the earth . . 150 



Weight of do. placed at a distance from Jupiter's 



centre equal to the semi-diameter of the earth . 150 x 1330 



Weight of do. removed to Jupiter's surface, the 150x1330 

 distance being thus increased 11 times . . 121 



If we perfoi m these arithmetical operations, multiplying 150 Ibs. 

 by 1.330, and dividing the product by 121 we shall obtain 

 1,648 Ibs. 



Thus it appears that if the materials ot which the planet 

 Jupiter is composed be similar to those of the earth, the weight 

 ot a man placed upon its surface would be greater than his 

 weight upon the earth, in the ratio of 1,648 to 150, or about 11 

 to 1, and of course the weights of all bodies would be greater in 

 the same proportion. 



It is evident, that although such a physical condition would not 

 at all exclude the possibility of Jupiter being an inhabited globe, 

 28 



