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Show 12 THE llODIES OP SPACE. under this pr!>cess, might,. by virtue of the greater solidity thence acquired, begin to pre~e~t sol?e re~nstance to th.e attractive force. As the sohd dicatwn proceeded, t~IS resistance would bPcome greater, though there would s~1ll be a tendency to adhere. Meanwhile, the condensation of the central mass 'vould be going on, tending to pr?d~cc a separation from what may no~ be termed the solzd~fying cru.st. During the contention between the attractiOn~ of these two bodies~ or parts c;f one body, there would probably be a ring of attenuahon betwPcn the mass and its crust. At length when the central ~a ~s ha~ reached a certain stage in its advance towards sol!ddicahon, a separation would take place, and the crust \vonld become a detached ring. It is clear, of course, that some law p~·esiding over the refrigeration of h~atcd .gaseous bodies would determine the stages at wh1ch nngs \vere thus formed and detached. We do not kno\v any uch law but what we have seen assures us it is one observing, and reducible to, mathen1atical formula. . If these rinO's consi ted of matter nearly umform throughout, they would probably continue e~ch in i~s original f~rm; ~ut ther~ ar? man?', chance ~gmnst their being umform In constitutiO_n. . I he unavoidable eflc~ts of irreO'ularity in their const1tutwn would he to cau:e them to o·~ther toward centres of superior solidity, by whtch the an~ular forn1 would, of com·s , be de troyed. The ring would in short break into several ma ses the largest of \Vhich' would e likely to attract the les ·cr into itself. The whole mass would then ncce~sar·ily. ettle int0 a sphe· rical form by virtue of the law of ~ravitation; in short, would then become a planet revolving round the sun. lt.-3 rotatory motion would, of course, continue_, and sate_l· lites mirrht then be thrown off in turn from Its body In exactly the same way as the primary planets had been thrown off from the sun. The rule, if I an be allowed so to call it, receives a strikinrr support from what app ars to be its exceptions. 1Vhile there are mat1y chance~ an·ainst the matter of the ring:-; being suflici ntly e9uable t~ l'cmain in the annular form till they were consolidated, it might nevertheless be othcn~· is il} some i.nstances; that i · to say, the equableness rn1o·ht, In those wstanc~s, be sufiiciently great. Such ''as }Jrobably tl~E:l case ~Jth the two ring."' arnuncl the body of 1aturn, wl11ch r:r:1a1n. a living picture of th~ arrangement, if not the cond1twn, HJ THEl.R ARRANGE.l\:fENTS .AND FORMATION. 13 which all the planetary masses at one tjme stood. It may also be admittecl that, when a ring broke up, it was possible that the fragments might spherify separately. Such seems to be the actual history of the ring between Jupiter and Mars, in whose place we now find four planets much beneath the smallest of the rest in size, and moving nearly a_t t~e same distance ~rom the sun, though in orbits so elhptrcal, and of such d1fferent planes, that they keep apart. It has been seen that there are mathematical proportions in the relative distances and revolutions of the planets of our system. It has also been suggested that the periods in the condensation of the nebulous mass, at which r~ngs were disengaged, must have depended on some par- . hcular crisis in the condition of that mass, in connexion with the laws of centrifugal force and attraction. M. ~omte, of Paris, has made some approach to the verification of the hypothesis, by calculating what ought to have been the rotation of the solar mass at the successive times when its surface extended to the various planetary orbits. He ascertained that that rotation corresponded in eve1·y case with the actual sidereal revolution of the planets, and that the rotation of the prirnary planets in like m.anner corresponded with the orbit'ltal periods of the secondaries. The process by which he arrived at this conclusion is not to be readily comprehended by the unlearned; but those who are otherwise, allow that it is a powerful support to the present hypothesis of the formation of the globes of spacE!·* l .,. M. Comte combined Huygens's theorems for the measures of centrifugal force with the law of gravitation, and thus formed a simple fundamental eqttation between the duration of the rotaUon of what he c.alls the producing star, and the distance of the star produce<. l. The constants of this equation were the radius of the central star, and the intensity of gravity at its surface which is a direct conseq_uence of its mass. It leads directly to the third law of Ke_~ler, which tht~s beco_mes susceptible of being conceived a p1'ion. In a cosmogomcal pomt of view. M. Comte first applied it to the moon .. and found, to his great delight, that the periodic time of that satellite agrees within an hour or two with the duration which the revolution of the earth ought to have had at the time when the lunar ~ist~nce formed the limit of the earth's atmosphere. He found the comc1dence less exact, but stili very striking, in every other case. In those of the planets he obtained for the duration of the correspon~Un~ so.lar rotations a value always a little less than their R?t!tal penod1c t1 m.es. " It is remarkable," says he, " that this difference, though mcreasing as the planet is more distant, pre• erves very nearly the same relation to the corresponding periodio • |