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Show JO ".l'P-E )JODIES OF SP AC}!. than half; Jupiter, 1 i 4 ; Mars, 3¥ ; Earth, 4! ; v·enu, 5}} ; Mercury, 9 iq_, or about the weight of lead. ThPn 1he distances are cu~·iously relative. It has been fol!lnd that if we place 1he following line of numbers- 0 3 . 6 12 24 48 96 192, and add 4 to each we shall have a series denoting the respective distances of the planets from the sun. It will stand thus- 4 7 10 16 28 52 100 196 Mere. Venus. Earth. Mars. Jupiter. Saturn. Uranus It will be observed that the first x·ow of figures goes on from the second on the left hand in a succession of du.J>lications, or multiplications by 2. Surely there is here a most surprising proof of the unity which I am claiming for the sola1· system. It was remarked '\Yhen this curious relation was first detected, that there was the want of a planet corresponding to 28 ; the difficulty was afterwards considered as in a great measure overcome, by the disc? very of four small planets revolving at nearly one mean d~stance from the sun, between Ma1·s and Jupiter. The distances bear an equally interesting mathematical relation to the times of the revolutions round the sun. It has been found that, with respect to any two planets, the squares o .. the ~imes of revolutions a~·e to each. other in the same proP. ortwn as the cubes of theu mean dis~ances-a most surpriSing result, for the discovery of which the world was indebted to the illustrious Kepler. Sir John Herschel truly observes " When ·we contemplate the constituents of the planetary system from the point of view which this rela- 'tion affords us, it is no longer mere analogy which strikes us, no longer a general resemblance arnong them, as individuals independent of each other, and circulating about the sun, ep.ch according to his own peculiar nature, and connected with it by its own peculiar tie. The resemplance is now perceived to be a true family likeness ; they are bound up in one chain,int€rwoven in one web of mutual relation and harmonious agreement, subjected to one pervading influence, which extends from the centre to the farthest limits of that great system, of which all of them, the Earth included, must henceforth be regarded a~ members.~t Connecting what has been observed of the series of nebulous stars with this wonderful relationship seen to • Astronomy, Lardner's Cyclopredia. THEIR ARRANGEMll;NTS AND FORMATION. ll exi~t among the constituents of our system, and further ~~king advantage of the light afforded by the ascertajned J..a,,-s of matter, modern astronomers have suggested the tolloV\tng hypothesis of the fcrmation of that system. . Of nebulous matter in its original state we know too l~t.tle t~ e~able us to suggest how nuclei should be estabhshe~ 1n.1t. But supposing that from a peculiarity in its cons!ItutiOn, nuclei are formed, we know very well how by VIr~ue of the law .of gravi~ation, the process of ·an ag~ gregahon of the neighbounng matter to those nuclei should proceed, until masses more or less solid should ~ecome detached froin the rest. It is a well known law 1n phy~ics that, when fluid 1natter collects towards or 1nrets In a centre, it establishes a rotary motion. See minor results of this law in the whirlwind anCJ. the whirlpo? l-nay, on so humble a scale as the water sinking ~hi ough the aperture of a funnel. n thus becomes cer... ain that when we arrive at the stage of a nebulous star we have a rotation on an axis commenced. ' Now, mechanical philosophy informs us that the instan~ a mas~ begins to rotate, there is generated a tendency to flii~g off Its outer portions-in other words, the law of centnfug~l fo!ce begir:ts. to operate. There are, then, two !orces acting 1n oppos1hon to eac.h other, the one attractIng tl!, the other throwing from, the centre. While these r~main ex.actly counterpoised, the mass necessarily continues ent~re; but the least excess of the centrifugal over the attr~ctlve force would be attended wit:lt the effect of separating the mass and its outer parts. These outer par~s w~uld then be le~t as a ring round the central body, '\-Vhwh nng would continue to revolve with the velocity possessed by the ~entral n;ta~s a~ the ~oment of separation, but not necessanly parbctpahng In any changes afterw~ rds undergone by that body. This is a_process which m1gh~ be repeated as soon as a new excess arose in the centnfugal over t~e att~·active forces working in the paren~ mass. It 1n1ght, Indeed, continue to be repeated, un!Il the niass attained the ultimate limits of the condensatwn w.hich it.s constitut~on _imposed upon it. From what cause might. anse the penod1cal occurrence of an excess o.f the centnfugal force ? If we suppose the agglomeration ?fa nebulo~s mass. to be a process attended by refrigeratwn. or cooling, which many facts render likely, we can easily understand why the outer parts, hardening |