20 CONSTITUENT MATERIALS OF THE EARTH, 



that matter is composed of infinitely minute particles or atoms, 

 each of which belonging to any one substance can only associate 

 with a certain number of the atoms of any other. There are 

 also strange predilections amongst substances for each other's 

 company. One will remain combined in solution with another, 

 till a third is added, when it will abandon the former arid at- 

 tach itself to the latter. A fourth being added, the third will 

 perhaps leave the first, and join the new comer. 



Such is an outline of the information which chemistry gives 

 us regarding the constituent materials of our globe, and their 

 combinations. How infinitely is the knowledge increased in 

 interest, when we consider the probability of such being the 

 materials of the whole of the bodies of space, and the laws 

 under which these everywhere combine, subject only to local 

 and accidental variations ! 



In considering the cosmogenic arrangements of our globe, 

 our attention is called in a special degree to the moon. 



In Laplace's Hypothesis, satellites are considered as masses 

 thrown oif from their primaries, exactly as the primaries had 

 previously been from the sun. The orbit of any satellite is 

 also to be regarded as marking the bounds of the mass of the 

 primary at the time when that satellite was thrown off; its 

 speed likewise denotes the rapidity of the rotatory motion of 

 the primary at that particular juncture. For example, the 

 outermost of the four satellites of Jupiter revolves round his 

 body at the distance of 1,180,582 miles; hence, according to 

 the hypothesis, the planet was about 7,083,492 miles in cir- 

 cumference, instead of being, as now, only 89,170 miles in 

 diameter. This large mass would take rather more than six- 

 teen days six hours and a half (the present revolutionary 

 period of the outermost satellite) to rotate on its axis. The 

 innermost satellite would be formed when the planet was re- 

 duced to a circumference of 309,075 miles, and rotated in 

 about forty-two hours and a half. 



From similar inferences, it would result that the mass of the 

 earth, at a certain point of time after it was thrown off from 

 the sun, was no less than 482,000 miles in diameter, being 

 sixty times what it has since shrunk to. At that time, the 

 mass must have taken rather more than twenty-nine and a 

 half days to rotate, (being the revolutionary period of the 

 moon), instead of, as now, rather less than twenty-four hours. 



The time intervening between the formation of the moon, 

 and the earth's diminution to its present size, was probably 



