186 Transactions. — Misfellaiieoils, 



In acTdition to the rotaiy motion in the plane of the paper, it will be 

 seen that, from the distribution of the attractions and of the matter, 

 pressure due to developed heat will act at first chiefly in a line passing 

 through the centre of gravity and perpendicidar to the plane of the paper, 

 so that doubtless, in the majority of cases, a considerable proportion of 

 gaseous matter will be found at the extremities of this axis. There appears 

 considerable evidence that this is really the case with nearly all the ring 

 nebulse. But more careful investigation is needed on this point, as the 

 drawings of different observers show considerable difference in this respect. 

 It is certain that in the visible Universe nebulous matter lies chiefly at the 

 poles of the galaxy. 



But the heat-motion acts in another way in addition to mere pressm-e. 

 Heat is caused by the motion of molecules, and this motion tends to give 

 an outward dii'ection to the whole mass of the gas. This motion tells most 

 in the lighter molecules, so that when any particle leaves its fellow, it 

 proceeds directly outwards away from the mass. This action, in many 

 cases, would doubtless convert the whole into a mere spheroidal shell, and 

 it is extremely probable that this is the condition of the planetary nebulae. 

 But whenever the ratio, struck off at coUision, is large, or there is a large 

 ratio of heavy molecules present, these latter return again and form the 

 star so often seen in the centre of these bodies. It would be worth while 

 for members to consider a variety of the many cases which partial impact 

 offers. A particularly interesting case is offered in which an impact is so 

 considerable that the escaping parts are mere shells, doubtless this would 

 break up, and strew the spiral with stars. And again, as regards the problem 

 of the subsequent state of the ends of the spindle, a careful inspection will 

 show that the forward velocity is very different on their two sides, doubtless 

 tending to cause them sometimes to separate into a number of rotating 

 masses, giving rise to multiple systems, having the peculiarity so charac- 

 teristic of the motion of our Solar System. 



Thus it appears that rotation, matter chiefly in one j)lane, and high 

 temperature proportional to mass, are the most striking general properties 

 in partial impact, but that the many modifying causes may sometimes 

 produce spirals or ruig systems, in other cases mere gaseous shells, or in 

 other cases densely-crowded systems, or complete dissipation of the whole 

 matter into space. In fact, the field of possibiUties appears nearly infinite. 



I think I have shown that it is almost certain that partial impact is at 

 once the most fi-equent of definite cosmical phenomena, and at the same 

 time a most powerful constructive agent in producuig the many marvels 

 which the monster tubes of the great astronomers have shown to exist in 

 such endless variety in the heavens. 



