]8 CONSTITUENT MATERIALS OF THE EARTH, 



large enjoyment of the sun's rays is no more than a compensa- 

 tion. Thus there may be upon the whole a nearly equal 

 experience of heat amongst all these children of the sun. 

 Where, meanwhile, is the heat once diffused through the 

 system, over and above what remains in the planets 1 May 

 it not have gone to constitute that luminous envelope of the 

 sun, in which his warmth-giving power is now supposed to 

 reside ? It may have simply been reserved to constitute, at 

 the last, a means of sustaining the many operations of which 

 the planets were destined to be the theatre. 



The tendency of the preceding considerations is to the con- 

 clusion that our globe is a specimen of all the similarly-placed 

 bodies of space, as respects its constituent matter and the 

 physical and chemical laws governing it, with only this quali- 

 fication, that there are possibly shades of variation with respect 

 to the component materials, and undoubtedly with respect to 

 the conditions under which the laws operate, and conse- 

 quently the effects which they produce. Thus, there may be 

 substances here which are not in some of the other bodies, and 

 substances here solid may be elsewhere liquid or vaporiform. 

 We are the more entitled to form such presumptions, since 

 there is nothing at all singular or special in the astronomical 

 situation of the earth. It takes the third place in a series of 

 planets, which series is only one of numberless other systems 

 forming one group. It is strikingly if such an expression 

 may be used a member of a democracy. Hence, we cannot 

 suppose that there is any peculiarity about it which does not 

 attach to multitudes of other bodies ; in fact, to all that are 

 analogous to it in respect of cosmical arrangements. 



It therefore becomes a point of great interest What are 

 the materials of this specimen ? What is the constitutional 

 character of this object, which may be said to be a sample, 

 presented to our immediate observation, of those crowds of 

 worlds which seem to us as the particles of the desert sand- 

 cloud in number, and to whose diffusion there are no conceivable 

 local limits ? 



The solids, liquids, and aeriform fluids of our globe are all, 

 as has been stated, reducible into fifty-five substances hitherto 

 called elementary. Of these, forty are well-characterized 

 metals, twelve non-metallic bodies, and the remaining three 

 solid substances of intermediate character, which form a con- 

 necting link between the two great groups. Among the non- 

 metallic elements, four viz., oxygen, hydrogen, nitrogen, and 



