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Show ; . _; ; .· . - .. -~ .. •).r • .' 1 I : • ' . 20 ~ONSTITUEN r MATERIALS CI' THE EARTH, tended by the condition of a very high temperature. The nebulous matter of space, previously to the formation of stPllar and planetary bodies, must have been a universal Fire Mist, an idea which "\Ve can scarcely comprehend, thongh the. reasons for arriving at it seem irl'esistible. The form,atwn of. syste~s out of this matter implies a change ot some ktnd With regard to the condition of the heat. Had this power continued to act with its full original repulsive energy, the process of ago-lomeration by attraction could not have gone on. W: do not know enough of the laws of heat to enable us to surmise how the necessary change in this respect was brought abou but we can trace some of the steps and consequences of the process. Uranus would be formed at the time when the heat of our system's rnatter 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 planets, Saturn being not more dense or heavy than the sub. sta~ce ?ork. It may be that a sufficiency of hear. still remains In those planets to make up for their distance from the sun, and the consequent smallness of the heat whic_h they derive. fro~ his rays. And it may equally ~e, since l\1e~cury Is twice the density of thP, earth, that Its matter exists under a degree of " cold for which that planet's larg~ enjoyment of the sun's l·ays is no more than a compensation. 'rhus there may be upon the whole, a nearly equal expenence of heat amongst all these children of the sua. Where, meanwhile, is the heat onca diffused through the system over and above what remaini in the planet~? May we n~t ratimw.lly presume it to hava gon.e to ~onstitute th_at. lurntnous _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 o~ into space-it must have simply been reserved to con~t1tute, at t~e last, a means of sustaining the many operatwns of \Vluch the planets were destined to be thQ theatre. . Th~ tend~ncy of the '~rh?le of the preceding consi-derations ts to b~-~~g the conviCtiOn ~hat our globe is a specimen of all_the similarly-placed bodJCs of space, as re~pects itg constituent matter and the physical and chemical laws governing it, with only this qualification, that there are vossib{y hades of variat~P"'. w.i!h respect to the component t.Uatenals, and undoubtedlv \Vtth resr,ect tu the conditions AND OF THE OTHER BODIES OF SPACE. 21 ~nder W?ich the laws operate, and consequently the ef .. fects whiCh they produce. 'thus, there may be substan· ces here. which are not in some other bodies, and substances here solid may be elsewhere liquid or vaporiform. 'Ve are ~he mo~e entitled t_o draw such cor;tch~sions,seeing.that there Is n~th1ng at all singular or special In the astronomical situation of the earth. It takes its place third in the series of planets, W:hich series is only one of numberless other systmes formi_ng one group. It is strikingly, if I may use such an expresswn, a member of a democracy. Hence, we cannot suppose that there is any peculiarity about it which does not probably attach to Inultitudes 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 t?e 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 ~hich seem to us as the particies of the desert sand-cloud In number, and to whose profusion there are no conceivable local limits? The solids, liquids, and aeriform fluids of our globe are a~l, as has been stated, reducible into fifty-five substances hitherto called .elementar.y. Six are gases; oxygen, hy{ h·ogen, and ~ntrogen being the chief. Forty-two are. met~l~, of whiC:h eleven are remarkable as composing, in c_omo1natw~ With oxyge~,. cert~in . earth~, as magnesia l~me, alum1n. The remaining six, Including carbon, silicon, sulphur, have not any general appellation. The ga3 oxygen is considered as by far the most abundant substance In our. globe. It constitutes a fifth part of o.ur atmospher~, a thn·d part of water, and a large proporhon of ever.y lund of rock in _the crust of the earth. Hydrogen, .w h1ch forms two-thu·ds of water' and enters into so~e mineral substances, is pethaps next. Nitrogen, of Nhl~h the atmosphere is four-fifths compo~ed, must be cons1dered as an abundant substance. The metal silicium ~~ich unites ~vith oxygen in nearly equal parts to form !Uhca, the basis of nearly half of the rocks in the earth's • c.rust, is, o~ cour~e, an jmportant ingredient. Aluminium !he metallic basis of alumin, a large n1aterial in many reeks, is another abundant elementary substance. So also, i~ carbon,_ a small i ngr.edicnt in the atmosphere, but the chief cons.\ttuen! of animal an~ vegetable substances, and of all fossiJ.s V.7hlCh ,ever were In the latter condition, ' |