62 THE PLURALITY OF WORLDS. 



powers of locomotion, this strength is regulated with reference to their weight, 

 and the extent and quantity of motion necessary for their well-being on the 

 surface of the globe. The structure of every animal is such, in the first place, 

 as to give it strength to support and move its own body ; but this is not enough ; 

 it must have a further amount of disposable force, to enable it to supply its own 

 wants by the pursuit of its prey ; by the collection of its food ; by the erection of 

 its dwelling ; and, in general, by its labor in the supply of its physical wants. 

 In the case of vegetables, the strength must be sufficient to support its weight, 

 and resist those external disturbances to which it is exposed such as -the ac- 

 tion of winds and other natural effects. But what, let us ask, regulates this 

 necessary quantity of strength ? What is the chief resistance which it has to 

 overcome 1 We answer, mainly the weight of the creature itself. But again ; 

 what is this weight ? It is a force produced by what ? By the combined at- 

 tractions of the whole mass of matter composing the globe of the earth, exer- 

 cised upon the matter composing the creature itself; thus the weight of a man 

 is merely the amount of the attraction of the globe of the earth exercised upon 

 the matter composing the body of the man. The amount of this attraction, 

 therefore, depends upon the quantity of matter in the earth ; but not on that 

 alone : it is a universal law of nature, that the energy of the attraction exerted 

 by matter, is increased with the proximity of the attracted body to the centre 

 of the attracted mass. Now if the matter composing the globe of the earth 

 were condensed into half its present bulk, all bodies placed upon the surface, 

 being proportionally nearer the centre, would be attracted with greater energy; 

 and, on the other hand, if the matter of the earth were swelled into a larger 

 bulk, the distance of objects on the surface from the centre being proportion- 

 ally increased, the energy of the attraction would be diminished. In the one case 

 the weights of all bodies would be augmented, and in the other they would be 

 diminished. The weights, then, of bodies placed on the surface of the earth, 

 depend conjointly in the mass of matter composing the earth, and on its 

 density. 



It is evident, then, that the adaptation which we see usually to prevail between 

 the strength of animals and plants and their weights, is, in reality, an exquisite 

 harmony which is maintained between the strength of these infinitely various 

 tribes of organized creatures, and the mass and density of the globe upon which 

 they are placed ; the slightest disturbance or change in this relation would 

 utterly derange the fitness of things, and would render the globe unfit for its 

 creatures, and its creatures unfit for the globe. The amount of attraction, or, 

 to use the more familiar term, the weight of the body on the surface of the 

 globe, is, then, an index, so to speak, to the organization of the creatures placed 

 upon the globe. If we would, then, inquire respecting the probable organiza- 

 tion of the dwellers upon the planets, one of the means of our inquiry would 

 be to ascertain what would be the weights of bodies upon their surfaces. Physi- 

 cal science enables us perfectly to accomplish this. The masses of matter 

 composing all the planets have been discovered with a great degree of precision. 

 Their magnitudes have also been measured. Now, to ascertain the weights of 

 bodies placed upon the surface of any of them, it is only necessary to consider 

 their masses and their magnitudes. The weight of a body placed upon any 

 planet is greater or less, caeteris parib us, than the weight of a body placed upon the 

 earth, just in proportion as the mass of matter in the planet is greater or less than 

 the mass of matter in the earth. If the distance from the surface to the centre of 

 the planet be double the corresponding distance in the case of the earth, then 

 the weight of bodies upon its surface would, on that account alone, be four 

 times less than in the case of the earth. But if, at the same time, the mass of 

 matter in the planet were sixteen times greater than the mass of matter in the 



