ON THE ORIGIN OF THE PLANETARY SYSTEM. 171 



fine dust, we see ourselves led to a primitive condition 

 of fine nebulous masses. 



From this point of view, that the fall of shooting- 

 stars and of meteorites is perhaps only a small survival 

 of a process which once built up worlds, it assumes far 

 greater significance. 



This would be a supposition of which we might 

 admit the possibility, but which could not perhaps 

 claim any great degree of probability, if we did not 

 find that our predecessors, starting from quite different 

 considerations, had arrived at the same hypothesis. 



You know that a considerable number of planets 

 rotate around the sun besides the eight larger ones, 

 Mercury, Venus, the Earth, Mars, Jupiter, Saturn, 

 Uranus, and Neptune; in the interval between Mars 

 and Jupiter there circulate, as far as we know, 156 

 small planets or planetoids. Moons also rotate about 

 the larger planets that is, about the Earth and the 

 four most distant ones, Jupiter, Saturn, Uranus, and 

 Neptune; and lastly the Sun, and at any rate the 

 larger planets, rotate about their own axes. Now, in 

 the first place, it is remarkable that all the planes 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 in these planes all the 

 rotation is in the same direction. The only consider- 

 able, exceptions known are the moons of Uranus, 



