310 



EXPLANATIONS 



ed by the orbit of Uranus. If this be the case, let it be 

 allowed as a difficulty. It is pointed out that the planets 

 do not increase regularly in density from the outermost 

 to the innermost. Their sizes are also not in a regular 

 progression, though the largest, generally speaking, are 

 towards the exterior of the system. It was not, perhaps, 

 to be expected that such gradations should be observed ; 

 but grant there was some reason to look for them, their 

 absence constitutes only another and a slight difficulty. 

 Then we know no law to determine the particular " stages 

 at which rings are formed and detached." Be it so — 

 although something of the kind there douDtless is, as the 

 distances of the planets, according to Bode's law, observe 

 a geometrical series of which the ratio of increase is 2. 

 From these objections, which cannot now be answered, 

 let us pass to some which can. 



It has been said that a confluence of atoms towards a 

 central point, as presumed by the nebular hypothesis, 

 would result, not in a rotation, but in a state of rest.* 

 According to the Morth British Review — " . . . Suppos- 

 ing the uniformly distributed atoms to agglomerate round 

 their ringleader, the space left blank by the slow advance 

 of the atoms in radial lines converging to the nucleus 

 must be a ring bounded by concentric circles, the outer 

 most circle being the limit of the nebulous matter not 

 drawn to the centre of the nascent sun. Now as all the 

 forces which act upon the agglomerating particles, 

 whether they proceed from the circumference of the un- 

 disturbed nebulous matter, or from the gradually increas- 

 ing nucleus, must have their resultants in the radial 

 lines above mentioned — there can be no cause whatever 

 capable of giving a rotatory motion to the mass. It must 

 remain at rest." 



Now there can be no doubt that a confluence proceed- 

 ing precisely to a centre has this result ; but this is only 

 an abstract truth, not an exact and absolute description of 

 any actual confluence of the kind. The explanation was 

 afforded by Professor Nichol, long before the objection 

 was started, and it could not be given in better language 

 on the present occasion : " When we reflect on the solar 

 nebula in the act of condensing, it appears that the act 

 consists in a flow or rush of the nebulous matter from all 



* North British Review, No. 6 Atlas Newspaper, Aug. 30, lS4b 



