1888.] of the various Species of Heavenly Bodies. 7 



Fig. 2. — Suggestion as to the origin of a globular nebula with a brighter central 

 portion. As in the former case, the luminosity of the fainter portion is due to 

 the collisions which occur along the sphere of intersection represented by the 

 larger circle. After collision the meteorites will travel in new orbits, and chere 

 will be an additional sphere of intersection, represented by the smaller circle. 

 The left-hand diagram is a cross-section, and the right-hand one represents the 

 appearance of the two collision- shells as seen from a point outside. 



gradually brighten towards the centre through collisions being possible 

 nearer the centre, and ultimately we shall have nebulas with a distinct 

 nucleus, the nucleus then representing the locus of most collisions. 

 This brightness may be sudden in certain spherical surfaces, or quite 

 gradual, according to the collision conditions in each swarm. 

 The final stage will be the formation of a nebulous star. 



Effects of Subsequent Rotation. — Spheroidal Nebulce. 



In such meteor- swarms as those we have considered, it must be that 

 rotation is, sooner or later, set up. Otherwise it would be impossible 

 to account for the spheroidal nebulas at all. I am aware that in 

 Newton's opinion the cause of this rotation was not mechanical, but 

 the moment we assume a meteoric origin of these globular clusters it 

 is straining the facts to assume that the intake will be exactly the 

 same at all points, and the moment the bombardment is more or less 

 localised, rotation must follow sooner or later. Sir William Herschel, 

 in his paper of 1811 (p. 319), says, " If we consider this matter in a 

 general light, it appears that every figure which is not already globu- 

 lar must have eccentric nebulous matter, which, in its endeavour 



