December. 1911. 



KNOWLEDGE. 



455 



increasing in intensit\' for ages, as the vast masses of 

 the two systems continue to crowd in upon one 

 another. In mj- earlv papier the name '"a.xial 

 extrusion" was sriven to this d\namical action. 



as we have said, in the opinion of Sir David Gill, 

 is a system of similar order to our Milky Way. 

 ^It should be understood that even in the case of 

 whirling; coalescence the central portion is the third 



Figure 1. 



The White Nebulae, largely double spiral, and Clusters in the Northern Hemisphere, plotted on eijual surface-projection 



by Mr. Sidney Walters, from Sir John Herschel's catalogue. The Nebulae are represented by dots, the Star Clusters by 



crosses. In this same belt are temporary, variable, double, and W'olf-Rayet stars. This belt is the MilUy Way. it contains 



the bulk of ordinary stars. Identically the same general distribution exists in the Southern Hemisphere. 



Presentl}" such an enormous quantit\' of material 

 has been expelled that the capturing i)ower of the 

 third bod\- diminishes. Selecti\e molecular escape 

 expels still more material, and the great central 

 furnace begins to burn itself out. This seems to be 

 the state of the great Nebula of Andromeda, which, 



body formed b\- the twi) coalescing portions. It 

 possesses the thermodynamic intensit\', and possesses 

 also the capturing power. When axial extrusion 

 occurs it ma\' be pointed out that the capturing 

 power diminishes, as it does in the formation of 

 the orbits of a double star. 



