The Theorif of Temporary >Stoy.s. 15 



velocities it demands would then be of the same order of magni- 

 tude as those concerned in the formation of comets' tails. If, 

 however, the parallax be too small for measurement — as has been 

 the case with all JVovae yet investigated — the ejection hypothesis 

 would be discredited, while the other grave objections to that of 

 Kapteyn and Wilson would still hold good. 



8.— Conclusion. The Origin of Temporapy Stars. 



The evidence collected in this paper does, as I think, disprove 

 the theory which attributes the spectroscopic phenomena to the 

 relative motion of difterent bodies, and shows them to be well 

 explained by ascribing them to disturbances in a gaseous mass. 

 That being .so, we must go further, and admit that the spectro- 

 scope throws no light on the origin of novae ; since it gives us no 

 inkling of the cau.se which impelled the star to suddenly rise 

 enormously in temperature and then clothe itself with fiery 

 vapours. 



The origin of the fiovae must therefore be discussed from 

 considerations other than spectroscopic. My own view is that 

 nothing we know of but collision is competent to originate a 

 fiova ; the only other assignable cause is chemical action within 

 the star, and I do not see how to reconcile a chemical hypothesis 

 with the facts, seeing that the star attained a temperature such 

 as probably no compound could experience without decomposition. 

 This conviction has been materially strengthened by a conversa- 

 tion with Professor Lyle, who gives it as his opinion that — even 

 in the most favourable ca.se — the generation of heat by chemical 

 action alone could not have been rapid enough to account for the 

 enormously sudden rise in luminosity.^ 



The final conclusion is, therefore, the following : — 



A collision — the direct evidence of which is not forthcoming — 



took place in the heavens, resulting in a great development of 



heat in the colliding masses ; this was followed by a tremendous 



outpouring, in all dii'ection.s, of incandescent gases. The subse- 



1 Williams's photographs of the region in the heavens in which the outbreak occurred 

 show (M.N. , l.\i., p. 337) that the star was below the 12th magnitude on 20th February; 

 hence its light must have increased at least 5000 times in less than 28 hours. 



