CONSTITUENT MATERIALS OF THE EARTH. 17 



occupying a vast deal more space than it formerly did. Some 

 of the gases, by being subjected to pressure, have become 

 liquids, or been solidified. Heat is a power greatly concerned 

 in regulating the volume and other conditions of matter. The 

 chemist will probably yet tell us what additional amount of 

 heat would be required to vaporize all the water of our globe ; 

 how much more to disengage the oxygen which is diffused in 

 nearly a proportion of one-half throughout its solids ; and, 

 finally, how much more would be required to cause the whole 

 to become vaporiform, which we may consider as equivalent 

 to its being restored to its supposed original nebulous state. 

 He may calculate with equal certainty, what would be the 

 effect of a considerable diminution of the earth's temperature 

 what changes would take place in each of its component 

 substances, and how much the whole would shrink in bulk. 



The earth and all its various substances have at present a 

 certain volume in consequence of the temperature which 

 actually exists. On the supposition that its matter and that 

 of the associate planets was at one time diffused throughout 

 the whole space now circumscribed by the orbit of the outer- 

 most planet, it follows, after what we know of the power of 

 heat, that the nebulous form of matter was attended by the 

 condition of a very high temperature. The nebulous matter 

 of space, previously to the formation of stellar and planetary 

 bodies, must have been a universal Fire Mist, an idea which 

 we can scarcely comprehend. The formation of systems out 

 of this matter implies a change of some kind with regard to 

 the condition of the heat. Had this power continued to act 

 with its full original repulsive energy, the process of agglome- 

 ration by attraction could not have gone on. We do not know 

 enough of the laws of heat to enable us to surmise how the 

 necessary change in this respect was brought about j but we 

 can trace some of the steps and consequences of the process. 

 Neptune would be formed at the time when the heat of our 

 system's matter was at the greatest, Uranus at the next, and 

 so on. Now this tallies with the exceeding diffuseness of the 

 matter of the outer planets, Saturn being not more dense or 

 heavy than the substance cork. It may be that a sufficiency 

 of heat still remains in those planets to make up for their 

 distance from the sun, and the consequent smallness of the 

 heat which they derive from his rays. And it may equally be, 

 since Mercury is nearly thrice the density of the earth, that its 

 matter exists under a degree of cold for which that planet's 



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