14 Proceedings of tlie Royal Society of Victoria. 



days ; had we, however, used 263 and 209 (or 5 and 4) as 

 divisors in drawing up Table III., instead of 8 and 7, the 

 discrepancies between the third and fifth columns would have 

 been serious/ Another difficulty is the brightening up of the 

 central patch of nebula, already mentioned as an obstacle in the 

 way of the collision theory ; to explain it on Kapteyn and 

 Wilson's hypothesis we should certainly have to assume an 

 increase of the star's luminosity at a late stage of its history, 

 which, as we have seen, probably did not occur. 



If we are prepared to go the length of supposing that the 

 substances forming the nebula were ejected from the star, we 

 shall find that this hypothesis accounts, better than the others, 

 for the facts above-mentioned. We may regard it as practically 

 certain that the rate of radial expansion of emitted gases would 

 diminish as the volume increased, hence the objections to 

 Kapteyn and Wilson's theory, based on Table III., do not apply 

 to this one, but rather tend to support it. Again, the 

 brightening of the central patch of nebula furnishes no difficulty 

 to the ejection hypothesis ; it may well be that the outflow from 

 the star, though immensely slowed down, is still going on — 

 possibly is intermittent ; but intermittence in the outflow does 

 not demand the same variation in luminosity as a new collision 

 or an actual revival of light, indeed the intermittent outflow 

 would probably hold the light-variations in check. In suggesting 

 this alternative hypothesis, I am fully conscious of its extrava- 

 gance ; this, however, is scarcely as great as it looks, on the 

 contrary the enormously rapid outgrowth of the tails of bright 

 comets — which are probably formed under the action of forces 

 immeasurably weaker than those at work in a Nova — seems to 

 give it some degree of plausibility. 



The question can hardly be settled until the star has been 

 examined for parallax. If this prove to be measurable, Kapteyn 

 and Wilson's hypothesis would be at (jnce disproved ; while the 

 ejection hypothesis would be somewhat strengthened, since the 



1 Kapteyn and Wilson both suggest that the discrepancy in the values of the star's 

 distance furnished by the earlier and later photographs maij be due to the inclination of 

 the nebula to the line of sight; but this can, I think, hardly hold good in the case of a 

 body whose greatest angular diameter is only a few minutes of arc. However that may 

 be, the objection stated above is a grave one. 



