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| [282] | The sun's neighbours still exercise their attraction over him |
| [283] | Regions of greatest density in the 9 nebulæ dealt with; compared with the |
| orbits of the planets made from them | |
| [287] | Results of comparison favourable to the theory |
| [289] | Differences of size in the planets have arisen from variations in the quantity |
| of matter accumulating on the nebulæ | |
| [290] | Causes of the retrograde motions in Neptune, Uranus, and their satellites |
| [292] | Probable causes of the anomalous position of Neptune |
| [293] | Rises and falls in the densities and dimensions of the planets explained |
| [295] | The form of the nebulæ must have resembled a dumb-bell |
| [296] | More about rises and falls in densities |
| [297] | Reason why the Asteroid nebula was the least dense of the system; |
| [298] | Not necessary to revise the dimensions given to the 9 nebulæ |
| [299] | Causes of the anomalies in the dimensions, densities, etc., of the Earth and Venus |
| [299] | The strictly spherical form of the sun accounted for. But it may yet be varied |
| [300] | Repetition that a spherical body could not be made from a lens-shaped |
| nebula by attraction and condensation |
Testing the Practicability of the Hollow Sphere Theory. Retrograde Motions, Positions, Densities, Masses, etc. etc., Considered.
Before going any farther it will be convenient to try to find out whether the solar system could have been constructed from a hollow nebula such as we have been describing gradually contracting as the matter for the formation of one planet after another was abandoned until—as we have put it—the nebula could abandon no more matter, and finally resolved itself into the sun. For this purpose we may suppose it to have been condensed and contracted until its extreme diameter was 6,600,000,000 miles; the same as we supposed it to have been, when we began the analysis of the nebular hypothesis. We will not now, however, suppose it then to have contained the whole of the cosmic matter out of which the system was formed, as we did before; because we have seen as we have come along that a very considerable part of that matter must have been left behind, almost from the moment that contraction commenced. We have already given the reasons for this in describing the domains of the sun; and, leaving the peaks out of account altogether for the present, we will only deal with the regions of what we have called the main body.
Although we have fixed a limit beyond which the neighbouring stars could not draw off any cosmic matter from the domains of the sun, that does not mean to say that their attractive powers would cease at that limit; because we have had to acknowledge that each one of them continues, even now, to exert its attractive power up to the very centre of the sun. They would still have power to counteract, in some measure, the sun's attraction of the matter of the nebula towards his centre, and the result would follow that there would be one or more, even many, fragments of the main body which would be left more or less behind, and in varied forms, when the more central part had contracted to the dimensions to which we have now reduced the nebula—all much the same as we have already said a few pages back.
When the nebula was 6,600,000,000 miles in diameter its volume would be 150,53324 cubic miles—as we have seen at [page 87]—the half of which is 75,26624 cubic miles, corresponding to a diameter of 5,238,332,000 miles, or radius of 2,619,166,000 miles. Now, according to our theory, it would be at this distance from the centre that the greatest density and activity of the nebulous matter would be, where we have just been showing how a movement of rotation could be generated, and where, in consequence, its motive power, so to speak, originated and existed. Here we find by dividing 5,238,332,000 by 6,600,000,000 that the region of greatest density in such a nebula would be at 0·7937 of its diameter. In our calculations about the earth, as it is, the proportion was found to be 0·7939, but the densities of the outer layers were empirically arranged by us; and, besides, almost the whole of the mass was supposed to be solid matter, so that no accurate result could be expected from that operation. There also we found that the inner surface of the hollow shell was at 0·5479 of the whole diameter, which we may adopt for the nebula we are about to deal with, as that dimension may be varied considerably—so may the other also—without in any way vitiating our theory.
Having found these proportions, which can only be considered as distantly approximate, let us go back to the 9 nebulæ—excluding the final solar one—into which we supposed the original nebula to have been divided—in the analysis just alluded to—and see how the regions of greatest density in them would correspond to the orbits of the planets formed out of them. This examination requires a good deal of calculation and accompanying description, which it might be found tiresome to follow, and would really answer no good end were it written out; so we shall suppose it to be made and the results obtained from the calculations to be represented in the form of [Table IX]., where they can be seen at a glance almost, and compared without much trouble. This arrangement will also furnish a readier means of reference for the remarks we shall have to make on, and the information obtained from, the examination. And we have still to add that the extreme diameters of the 9 nebulæ are the same as those we used for the analysis; as also, that we make use of only the first of the proportions just cited, viz., 0·7937, it being the only one required for determining the positions of the regions of greatest density in the nebulæ.
[TABLE IX.].— Dimensions of the nine Nebulæ, with their Diameters and Regions of greatest Density compared with the Diameters of the Orbits of the Planets formed from them.
| Nebula. | Region of Greatest Density. | Orbit of Planet. | Region of Greatest Density compared with Orbit. | |||||
| Name of Planet. | Outer Diameter (Miles). | Diameter (Miles). | Radius (Miles). | Diameter (Miles). | Radius (Miles). | Within (Miles). | Without (Miles). | Per cent. |
Neptune | 6,600,000,000 | 5,238,332,000 | 2,619,166,000 | 5,588,000,000 | 2,794,000,000 | 174,734,000 | — | 6·26 |
| Uranus | 4,580,000,000 | 3,635,146,000 | 1,817,573,000 | 3,566,766,000 | 1,783,383,000 | — | 34,190,000 | 1·92 |
| Saturn | 2,672,000,000 | 2,120,766,400 | 1,060,383,200 | 1,773,558,000 | 886,779,000 | — | 173,604,200 | 19·58 |
| Jupiter | 1,370,800,000 | 1,088,003,960 | 544,001,480 | 967,356,000 | 483,678,000 | — | 60,323,480 | 12·47 |
| Asteroids | 744,000,000 | 590,512,800 | 295,256,400 | 520,600,000 | 260,000,000 | — | 35,256,400 | 13·56 |
| Mars | 402,000,000 | 319,067,400 | 159,533,700 | 283,300,000 | 141,650,000 | — | 17,883,700 | 12·63 |
| Earth | 234,620,000 | 186,217,894 | 93,103,947 | 185,930,000 | 92,965,000 | — | 138,947 | 0·15 |
| Venus | 160,210,000 | 127,158,677 | 63,579,339 | 134,490,000 | 67,245,000 | 3,665,660 | — | 5·45 |
| Mercury | 103,230,000 | 81,933,651 | 40,966,825 | 71,974,000 | 35,987,000 | — | 4,979,825 | 13·84 |
Had the position of Neptune been normal, the above data for him and Uranus would have been as under. More or less. | ||||||||
| Neptune | 8,299,786,830 | 6,587,540,800 | 3,293,270,000 | 5,588,000,000 | 2,794,000,000 | — | 499,270,000 | 17·86 |
| Uranus | 5,144,439,613 | 4,083,042,000 | 2,041,521,000 | 3,566,766,000 | 1,783,383,000 | — | 258,138,800 | 14·48 |