200 Tra)isactioiis. — Miscellaneoas. 



In my paper on the Visible Universe,'-'' I have given reasons to show that 

 possibly the whole of the galactic poles consist of more or less diffused 

 nebulous matter. As the reasoning, upon which I based this conclusion, 

 appears to have been too condensed to be readily understood, I will give 

 it a a little more in detail. Suppose the plane of the paper to contain 

 the orbits of the two impacting bodies ; when dming the impact the centres 

 of the two bodies are at their nearest point, it is probable the gaseous 

 pressure produced by the impact will be near its maximum. It is certain 

 that this pressure can only cause an escape of gas in a plane perpendicular 

 to — and bisecting — the line joining the two centres of the two spheres. 

 But the chief part of the material left by unbalanced momentum will be 

 in the intersection of this plane and the plane of the paper, hence the only 

 direction in which the pressure can act will be in a direction perpendicular 

 to the plane of the paper. But this direction is the same as the axis of 

 the resultant rotation due to the impact, and perpendicular to the plane in 

 which the general mass of the matter will be distributed (which is clearly 

 the plane of the paper). After the central mass has become free from the 

 two bodies, the pressure will act in all directions, but the gas extended 

 during the impact will more or less continue the direction it has taken, 

 and will, doubtless, to a large extent separate itself from the other portions. 

 As its direction will be perpendicular to the general movement, the polar 

 nebular caps, and not '"unhkely all annular nebulas which accompany the 

 galaxy, were probably so formed. 



Having thus shown that the poles of the milky way were probably at 

 one time covered with diffused nebulous matter, I will discuss the mode in 

 which aggregations may be formed. It appears certain that any very large 

 cosmical bodies would have myriads of bodies travelling around them in aU 

 orbits. In the case of the two large bodies which formed the Universe, it 

 would, therefore, probably be so likewise. Many of these bodies would be 

 entrapped by the outrushing gas, and would be carried with it in its journey. 

 The gas would also meet the bodies already existing in the portion of space 

 through which it travelled. At first, the temperature would be so high 

 that the smaller bodies would certainly be heated and volatilized, but 

 would render the mass more or less irregular, and these irregularities, if 

 very considerable, would tend to increase themselves. The larger masses 

 might form permanent nebulae ; in some cases, these would ultimately 

 become stars. As the nebulous mass became colder, a pecuUar selective 

 action would not improbably tell upon it. If the temperature of the mass 

 be uniform, the velocity of mean-square of the molecules of the ■ several 

 chemical elements will be inversely as the square-root of these molecules' 

 weight. A body traveUing through this mass may have sufficient attractive 



* Vide ante, Ai-t. XIII. 



