20 CONSTITUENT MATERIALS CF THE EARTH, 



tended 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, 

 though the reasons for arriving at it seem irresistible. 

 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 ori- 

 ginal repulsive energy, the process of agglomeration 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, 

 but we can trace some of the steps and consequences of 

 the process. Uranus w r ould be formed at the time when 

 the heat of our system's matter was at the greatest, Saturn 

 at the next and so on. Now this tallies perfectly with 

 the exceeding diffuseness of the matter of those elder pla- 

 nets, Saturn being not more dense or heavy than the sub- 

 stance cork. It may be that a sufficiency of hear still re- 

 mains 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 twice the density of the earth, that 

 its matter exists under a degree of cold for which that 

 planet's large enjoyment of the sun's rays is no more than 

 a compensation. Thus there may be upon the whole, a 

 nearly equal experience of heat amongst all these chil- 

 dren of the sun. Where, meanwhile, is the heat once 

 diffused through the system over and above what remain* 

 in the planets ? May we not rationally presume it to have 

 gone to constitute that luminous envelope of the sun, in 

 which his warmth-giving power is now held to reside. It 

 could not be destroyed — it cannot be supposed to hava 

 gone off into space — it must have simply been reserved 

 to constitute, at the last, a means of sustaining the many 

 operations of which the planets were destined to be tha 

 theatre. 



The tendency of the whole of the preceding considera- 

 tions is to bring the conviction that our globe is a specimen 

 of all the similarly- placed bodies of space, as respects ita 

 constituent matter and the physical and chemical laws 

 governing it, with only this qualification, that there are 

 vossibly shades of variation with respect to the component 

 materials, and undoubtedly with respect to the conditions 



