.OPULAU sci:::rnnc LIXTURES. 



CS9 



in space, being probably thoso vliicli hnvo 

 ftlready undergone disturbances by planets. 

 There are also denser swarms which move in 

 regular elliptical orbits, cutting the earth's 

 orbit in definite places, and therefore always 

 occur on particular days of the year. Thus 

 the 10th of Augiist of each year is remarkable, 

 and every thirty-three years the splendid fire- 

 works of* the 12th to the 14th of November 

 repeats itself for a few years. It is remark- 

 able that certain comets accompany the paths 

 of these swarnis, and give rise to the suppo- 

 sition that the comets gradually split up into 

 meteoric swarms. 



This is an important process. What tho 

 earth does is dona by the other planets, and 

 in a far higher degree by the sun, toward 

 which all the smaller bodies of our system 

 must fall ; those, therefore, that are more 

 subject to the influence of tho resisting medi- 

 um, and which must fall the more rapidly, 

 the smaller they are. The earth and tho 

 planets have for millions of years been sweep- 

 ing together the loose masses in space, and 

 they hold fast what they have once attracted. 

 But it follows from this that the earth and 

 the planets were once smaller than they are 

 now, wl that more mass wrw diffused in 

 Bpaco ; and if we follow out this considera- 

 tion it takes us back to a state of things in 

 which, perhaps, all the mass now accumulat- 

 ed in the sun and in the planets, wandered 

 loosely diffused in space. If wo consider, 

 further, that the small masses oi! meteorites 

 as they now fall, have perhaps been formed 

 by the gradual aggregation of fine dust, wo 

 BOO ourselves led to a primitive condition of 

 fine nebulous masses. 



From this point of view, that tho fall of 

 ehooting-stars and of meteorites is perhaps 

 only a small survival of a process which onco 

 built up worlds, it assumes far greater sig- 

 nificance. 



This would be a supposition of which \vo 

 might admit the possibility, but which could 

 not perhaps claim any great degree of prob- 

 ability, if we did not find that our prede- 

 cessors, starting from quite different con- 

 siderations, had arrived at the same hypoth- 

 ecis. 



You know that a considerable number of 

 planets rotate around tho sun besides tho 

 eight larger ones, Mercury, Venus, the Earth, 

 Mars, Jupiter, Saturn, Uranus, and Nep- 

 tune ; in the interval between Mara and Ju- 

 piter there circulate, as far as we know, 156 

 small planets or planetoids. Moons also 

 rotate about the larger planets that is, about 

 the Earth iind the four most distant ones, 

 Jupiter, Saturn, Uranus, and Neptune ; and 

 lastly tho Sun, and at any rate tho larger 

 planets, rotate about their own axes. Now, 

 in tho first place, it in remarkable that all 

 the pianos of rotation of the planets and of 

 their satellites, as well as the equatorial 

 planes of these planets, do not vary much 

 from each other, and that ill those planes all 

 the rotation is in tho same direction. Tho 

 only considerable exceptions known are tho 

 moons of Uranus, whoso plane i.* almost ut 



right angles to the planes of the larger plan- 

 ets. It must at the same time be remarked 

 that the coincidence, in tho direction of 

 these planes, is on tho whole greater, the 

 longer are the bodies and the larger the paths 

 in question ; while in the smaller bodies, and 

 for the smaller paths, especially for tho 

 rotations of the planets about their own axes, 

 considerable divergences occur. Thus tho 

 planes of all the planets, with the exception 

 of Mercury and of the small ones between 

 Mars and Jupiter, differ at most by three 

 degrees from the path of the Earth. The 

 equatorial plane of tho Sun deviates by only 

 seven and a half degrees, that of Jupiter only 

 half as much. The equatorial piano of the 

 Earth deviates, it is true, to the extent of 

 twenty-throe and a half degrees, and that of 

 Mars by twenty-eight and a half degrees, and 

 the separate paths of the small planet's satel- 

 lites differ still more. But in these paths they 

 all move direct, all in the same direction about 

 tho sun, and, as far as can be ascertained, 

 also about their own axes, like the earth that 

 is, from west to east. If they had originated 

 independently of each other, and had come 

 together, any direction of the planes for 

 each individual one would have been 

 equally probable ; a reverse direction of tho 

 orbit would have been just as probable as a 

 direct one ; decidedly elliptical paths would 

 have been as probable as the almost circular 

 ones which we meet with in all the bodies we 

 have named. There is, in fact, a complete 

 irregularity in the comets and meteoric 

 Gwarms, which we have much reason for con- 

 sidering to be formations which have only 

 accidentally come within the sphere of tha 

 sun's attraction. 



Tho number of coincidences in the orbits 

 of tho planets and their satellites is too great 

 to be ascribed to accident. We must in- 

 quire for the reason of this coincidence, and 

 this can only be sought in a primitive con- 

 nection of the entire mass. Now, we are ac- 

 quainted with forces and processes which 

 condense an originally diffused mass, but 

 none which could drive into space such largo 

 masses, as the planets, in the condition we 

 now find them. Moreover, if they had be- 

 come detached from the common mass, at a 

 placo much nearer the sun, they ought to 

 have a markedly elliptical orbit. We must 

 assume, accordingly, that this mass i:i its 

 primitive condition extended at least to tho 

 orbit of the outermost planats. 



These were the essential features of th> 

 considerations which led Kant and Laplaco 

 to their hypothesis. In their view our sys- 

 tem was originally a chaotic ball of nebulou.i 

 matter, of which originally, when it extended 

 to the path of the most distant planet, many 

 billions of cubio miles could contain scarcely 

 a gramme of mass. This ball, when it had 

 become detached from tho nebulous balls of 

 fue adjacent fixed rtars, possessed it slow 

 movement of rotatiof It became condensed 

 under the influence 1 l he reciprocal attrac- 

 tion of its parts ; an \ the degree in which 

 it condensed, tho rr motion increased, 



