102 F. W. Very— A Cosmic Cycle. 



matched classes of solar stars, one on an ascending and the 

 other on a descending scale of temperature, as in Lockyer's 

 classification; but each stage is passed through once for all, 

 and the order of transition is as follows : 



(A) Stars typically of great mass but small density. 



(A a ) Bright-line Orion stars, but little removed from nebu- 

 lae. Hot and rarefied, but the heat somewhat uniformly dis- 

 tributed by free convection. 



(A 2 ) Orion stars with narrow dark hydrogen and helium 

 lines. Hot and more condensed, but not to such an extent as 

 to separate an extensive hydrogen atmosphere ; moreover, 

 metalloids prevail over metals. All of these may be looked 

 upon as explosive stars, if of sufficient magnitude, giving rise 

 to clusters and extensive nebulae with intimate physical and 

 chemical connection between stars and nebulous matter. 



By the subdivision of these stars of great mass, a new stage of 

 quiescent development is begun in which small mass and thence 

 small pressure, with viscosity, prevent disruptive explosion. 



(B) Stars typically of smaller mass and of relatively great 

 condensation. 



(B x ) Sirian stars. A dense hydrogen atmosphere. Conden- 

 sation begun, but not yet very great. 



(B 2 ) Frocyon stars. More condensed. Interior convulsions 

 begin to bring up denser material and mingle it with the outer 

 layers. 



(B 3 ) Solar type. Still more condensed, and very hot at the 

 core. Complex spectra. Calcium and metals prevail. 



(B 4 ) Stars with unknown flutings of absorption, growing 

 fainter towards the red, indicating tiie presence of complex 

 molecules. Variable from outbursts* of hot luminous gases. 



(B 5 ) Stars with dark hydro-carbon absorption flutings, 

 growing fainter towards the violet. First appearance of com- 

 pounds. Central condensation probably extreme, and near the 

 limit of possible stellar life. 



Stage (A 2 ) corresponds to McClean's Div. 1, to Lockyer's 

 A a and A 7 , and to Miss Maury's Groups II to Y. "The 

 helium stars of Division 1 and the gaseous nebulae are sub- 

 ject to a similar law of distribution in relation to the galactic 

 plane."" 



Condensation and development of heterogeneity go hand in 

 hand. Explosive forces, no longer strong enough to disrupt, 

 are gradually resumed in stage (B), and are perhaps responsi- 

 ble for the equally gradual disappearance of hydrogen. 



Nebulae and novae are obviously near to (A,). The Orion 

 stars, as stated, sometimes have bright lines in their spectra, 

 the hydrogen being negatively electrified. In this group come 



*F. McClean, Phil. Trans. R. Soc, London, vol. cxci, p. 129, 1898. 



