220 Prof. A. W. Bickerton on Cosmic Evolution. 



Hydrogen at the same temperature has sixteen times the 

 tendency to escape that oxygen has, and two-hundred and 

 eight times that of lead. This tendency of the chemical 

 elements to sort themselves I call " selective molecular 

 escape." 



Hence at every cosmic impact of dense bodies some light 

 molecules leave with such extreme velocity as to escape not 

 merely the mass, but the galactic system altogether. These 

 molecules wander in space, perchance to other cosmic systems. 



Another agency is at work giving motion to free molecules. 

 Radiant energy is caught by cosmic dust of all dimensions. 

 Sir W. Crookes's experiments on " Radiant Matter " suggest 

 that free molecules do not take up or give out radiation. 

 (Dr. Johnstone Stoney has lately suggested to me that this 

 point is unimportant, as even should the molecules absorb 

 radiation, this energy will increase the velocity of the suc- 

 ceeding rebound.) But when slowly moving light molecules 

 touch this heated dust, it will bound off in the same way 

 that molecules fly with increased velocity from radiometer- 

 vanes. Thus radiant energy is converted into heat, and this 

 into potential energy. 



There are other agencies by which light atoms are liberated 

 from cosmic systems to wander indiscriminately. Such 

 atoms do work against the attraction of systems, and where 

 potential is highest they move slowest. 



Where they thus linger they tend to accumulate. The 

 potential of this part of space lessens, and the work required 

 to reach these positions not being so great as at first, oxygen 

 and other heavier molecules get there, increasing the density; 

 and oxygen also tends to produce non-volatile compound 

 molecules. 



These would coalesce ; but helium and the other cosmic 

 pioneers do not combine, they remain permanently gaseous. 

 Thus a primary cosmic system is incipient. Dense bodies 

 sent out of cosmic systems by the interaction of three bodies 

 would generally pass through old cosmic systems where matter 

 is in dense masses, but evidently not through such vast 

 gaseous aggregations as the incipient cosmic systems. The 

 bodies would be retarded by the friction produced, and 

 perchance volatilized, forming nucleii in the general mass ; 

 their mutual attraction would cause denser aggregations to 

 occur, and a cosmic system of the first order would be 

 produced. Two such systems colliding produce a system of 

 the second order. This, colliding with any other cosmic 

 system, produces a system of the third order. Our own 

 galactic system is very probably a tertiary system. 



