TABLE III.—Continued.

At Density of Water
Dimensions of Rings.		At Air Density
Space to Grain of Matter.
Name.Times less Dense than Air.Absolute Temperature (Degrees).Breadth (Miles).Thickness (Miles).Avg. Thickness (Miles).Cubic Feet.Side of Cube (Feet).Inches
Neptunian
403,000,000
0·00000068



713,223
89·327
1,010,000,000511,794341,196

Uranian
134,710,620
0·000002034
954,000,000
252,193
100,553
238,357
61·994

Saturnian
26,750,876
0·00001024
650,600,000
881,037
238,000
47,313
36·168

Jovian
3,613,182
0·00007583
313,400,000
1,406,771
450,282
6,303
18·472

Asteroidal
578,254
0·00047384
171,000,000
588
185
1,023
10·075

Martian
91,259
0·00300244
83,690,000
152
61
161
5·445

Earth
18,134
0·0151097
37,205,000
961
612
32
3·178

Venus
5,774
0·047454
28,489,000
420
225
10·2
2·170

Mercurian
1,545
0·1773463
20,000,000
25
11
2·734
1·398

Solar







3550·771831 0·62830·856510·28
2740·99635 0·48480·78569·43
02·0000 0·001770·1211·452

Returning now to [page 84], we see that the volume of the sun alone was considered to be 482,16912 cubic miles, which corresponds to a diameter of 972,869 miles. Comparing this with the volume 482,16712 cubic miles, ([see page 99]), left after all the members of the Solar system have been separated from the original nebula, we find that there is a remainder of 2,000,000,000,000 cubic miles less than we ought to have. But it will be remembered that we added only 1/700th part to the mass of the sun for the mass of the whole Solar system, whereas it will be seen, by referring to [Table II]., that we ought to have added 1/696·86th part. Had we done so the sphere containing the whole Solar system at the density of water would have been 973,361·31 miles in diameter with volume of 482,860,7449 cubic miles, which would have added 3,153,681,000,000 cubic miles to the volume we started with, and would have left us with 1,375,903,430,000 cubic miles more than we ought to have had. Besides, for the sake of round numbers, we made the diameter of the nebula containing the whole Solar system, at the density of water, to be 973,360 instead of 973,359·208 miles, and thereby really added more to the original volume than we should have; so that the defects in accuracy at the beginning of our work partially counterbalanced each other, which accounts so far for the difference noted at the end not being much more than half of what it should have been. Taking all this into consideration, and the really insignificant magnitudes of the differences that would result from the corrections that could be made, we have not thought it necessary to reform the whole of our calculations. Besides, the data we have been working upon are not so absolutely exact as to insure us that we should get nearer to the truth by making the revision. The whole error would be much more than obliterated were we to apply 5·67 instead of 5·66 for the mean density of the earth to the debit side of the sun's account.

To simply describe arithmetical operations conveys no really satisfactory meaning to the mind; of working them out in full there is no end; and to partially represent them as we have done in these pages, although showing how the results are arrived at, still leaves them so mixed up together that it is difficult to compare them with each other, and to note the sequences from the beginning to the end of the whole operation. For these reasons we have compiled [Table III]., where the whole of the principal and most important data, and results from them, may be followed out and examined.

We may now say that we have taken our nebula to pieces, with the exception of the parts belonging to the satellites of those planets which have them; which would only be a tiresome repetition of what we have done for each principal member of the system, provided we had the necessary data, which we have not; and have thus acquired a certain amount of knowledge of the primitive conditions of each one of them. But we have still to examine into and draw conclusions from what we have seen and learned during the operation; which in some points, differ very much from our notions, formed from what we had previously read on the subject.

[CHAPTER VI.]

Page
[108]Analysis continued. Excessive heat of nebula involved condensation only at
  the surface. Proof that this was Laplace's idea
[109]Noteworthy that some astronomers still believe in excessive heat
[110]Interdependence of temperature and pressure in gases and vapours.
  Collisions of atoms the source of heat
[110]Conditions on which a nebula can be incandescent. Sir Robert Ball
[112]No proper explanation yet given of incandescent or glowing gas
[115]How matter was thrown off, or abandoned by the Jovian nebula
[116]Division into rings of matter thrown off determined during contraction
[117]How direct rotary motion was determined by friction and collisions of particles
[118]Saturn's rings going through the same process. Left to show process
[120]Form gradually assumed by nebulæ. Cause of Saturn's square-shouldered appearance
[120]A lens-shaped nebula could not be formed by surface condensation
[121]Retrograde rotary motion of Neptune and Uranus, and revolution of their satellites
  recognised by Laplace as possible
[123]Satellites of Mars. Rapid revolution of inner one may be accounted for
[124]Laplace's proportion of 4000 millions not reduced but enormously
  increased by discoveries of this century