SUPERFICIAL MAGNITUDE. 



is 1,330 times that of the earth ; and that those of Saturn. Uranus, 

 and Neptune are respectively 857, 88, and 107 times that of 

 the earth. 



To render these vast proportions more clearly perceptible, we 

 have represented them in the annexed figures. If E (fig. 4) be 

 imagined to represent the globe of the earth, the globe of Jupiter 

 will be represented on the same scale by J, that of Saturn by s, 

 that of Uranus by u, aud that of Neptune by N. 



21. If they be inhabited globes analogous to the earth, they 

 will accommodate a population as many times greater than that 

 to which the earth is adapted, as their surfaces are greater than 

 the surface of the earth ; and since the surfaces of globes are in 

 the proportion of the squares of the diameters, Jupiter would 

 afford space for habitation 121 times greater than the earth, and 

 Saturn 90 times, Uranus 18 times, and Neptune 23 times greater. 



22. It may, however, be asked whether this vast difference 

 in the magnitude of these globes compared with that of the 

 earth may not involve some physical consequences incompatible 

 with the supposition of their being habitable globes at all 

 analogous to the earth. 



There is but one such consequence at all conceivable. It is 

 that the effects of gravity upon them might be such as to be 

 altogether unfitted for species organised like those of the earth. 

 Thus, upon the earth the average strength of a man is adapted 

 to support and give freedom of motion and action to a body 

 whose average weight is an hundred and a half; that of a 

 horse to one whose average weight is half a ton, and the like ol 

 other animals. The strength of the stalks and trunks of vege- 

 tables is in like manner adapted to their weights. In the same 

 manner the materials of artificial structures have a strength 

 which has like relation to their weights. 



If these species, animal and vegetable, and these artificial 

 structures were suddenly transferred to the surface of a planet, 

 on which they would have several hundred times their present 

 weight, the animals would not only be totally incapable of loco- 

 motion, but they, as well as the vegetables and artificial 

 structures, would be crushed and crumbled to pieces under the 

 enormous pressure of their own weights. 



In discussing this question, it is therefore of the greatest 

 importance to inquire whether the vast dimensions of this group 

 of planets may not cause an increase of weight of bodies 

 plai-ed upon their surfaces so immense as to destroy all analogy 

 to the earth considered as an inhabited globe. 



In answer to this question, it may be replied that the weight of 

 bodies placed upon the surface of a globe will depend conjointly 



27 



