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Show 22 CONSTITUENT MATERIAl" OF THE EARTH, amongst \"'vhich coal takes a cons~icuous pl.ace. The fa· ntiliarly-known metals, as iron, hn, lea.d, s1l':er, gold, art elements of contparatively sma~l magnitude In that. exterior part of the earth's body which w~ u.i·e able to Inves-tigIatt ei.s remarkable of the simple substances th at th ey ai· e generally in some compound form. Thus,. oxygen and nitrogen, though in union they form t~e aenal envelope of the globe, are never found separ~te In nature: Carbon is ure only in the diamond. And the metallic bases of th~ earths, though the chemist can ?isengage them,, may well be supposed unlikely to remain long uncombined, seeing that contact with moisture ~al~es them burn. Combination and re-combination are pnnciples largely pervading natnre. There are few rocl~s, For exatnple, that arf not composed of at least two vanebes of matter, each o which is again a compound ~f elementary su_bsta~ce~. Wl t · s still more wonderful With respect to this pnncl-le1~ f ~ombination, all the el~men~ary s11_bstan?es observe ~ertain mathematical proportions In then unwns. One volume of them unites with one, ~wo, t~uee, or more volumes of another, any extra quant~ty being sure to be left over if such there should be. It _Is hence .supposed that matter is c~~posed of infinitely minute parttcles or atoms, each of which belonging to any one sub.stance, can only (through the operation of some as yet h1dden law) as~;;ociate with a certain number of the atoms of any oth~r. There are also strange predilec~ions am?nst sub~tanc~s for each other's compan:y. On_e ~Ill remain com:tnn~d In solution with another, till a thud IS added, when It w1ll abandon the former and attach itself to the latter. A fourth.b~ing added, the third will perhaps leave the first and JOin the new comer. . h' h h · t Such is an outline of the informatiOn yv 1c c em1s ry give:., us re~arding the con tituent ~atenals of. ou~· globct Hmv infinitely is the knowl dge Increase~ In 1nteres when we consider the probability of such bemg the material. of the \V hole of the bodies of ~pace, a~d the laws under which these everywhere combine, subject only to lo-cal and accidental variations. . In considering the cosmog.onic arrangements of our globe, our attention is called In a speci'll degree to tbe m~~~the nebular hypothe_is, satellites a.re considered M AND )F TH:JU.. OTHER BODIES OF SPACE. 23 masses thrown off 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 r~pidit~ 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 d~tance of 1,180,582 miles, showing that the planet was once 3,675,501 miles in circumference, instead of being as now only 89,170 miles in diameter. This large mass took rather more than sixteen days six hours and a half (the present revolutionary period of the outermost satellites) to rotate on its axis. The innermost satellite must have been formed when the planet was reduced to a circumference of 309,075 miles, and rotated in about forty-two hours and a half. From similar inferences, we find that the mass of the earth, at a ce~tain point of time, after it was thrown otr from the sun, was no less than 482,000 miles in dian1eter being sixty times what it has since shrunk to. At that ti!lle the mass must have taken rat~er more than twentynine 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 one of those vast sums in which astronomy deals so largely, but which the mind altogether fails to grasp. The observations made upon the surface of the moon , by telescopes _tend strongly _to support the hypothesis as to all the bodies of space being com posed of similar matters subj~ct ~o cert~in var~ations. It does not appear that our satellite Is provided w1t~ that gaseous envelope which, ~:m earth, performs so many Important functions. Neither, Is there any appe~rance of water upon the surface; yet that. s_urface Is, hke that of our globe, marked by inequahtte. s nnd _t~1e appearanc~ of volcanic operations. These Inequalities and volcaniC operations are· upon a scale far greater than any which now exist upon the ea.rt~'s _surface. _Althoug~, from the greater force of gravitation upon Its extenor, the mountains other circumstances being equal, might have been expected to be much smaller than ours, they are, in many instancea, |