378 Professor H. H. Turner [June 5, 



Nature of New Stars. 



When I pass from this account (however imperfect) of the 

 discovery of new stars to consider what they are, it is like leaving 

 firm ground for quicksand. The inquiry is at present in that stage 

 which is sometimes summed up by the daily papers in the phrase, 

 " The police have a clue and are investigating the matter." The 

 astronomical police think they have a clue, or rather several clues, 

 to the origin of these outbursts, and various able members of the 

 force are diligently investigating the matter ; but they are as yet far 

 from being able to prove their case against any suspected agency. 

 The culprits to whom the evidence seems to point are the nebulae — 

 in almost every instance where it has been possible to collect 

 information, a nebula appears if not definitely as the originator of 

 the outburst, at least as an accessory after the fact. The new star 

 of 1885 appeared in the midst of the nebula in Andromeda as we 

 have seen ; and one of those found at Harvard (Nova Centauri, 1895) 

 also originated within a visible nebula. 



The suggestion I wish to make to the jury is that in other cases 

 also, although nebulae could not be seen, they were really there. And 

 I proceed to give evidence in support of this view. 



Firstly, it is quite certain that some nebulae are not seen merely 

 because they are too faint for our present telescopes. For as 

 telescopes have increased in power, and plates in sensitiveness, and 

 exposures in duration, more and more nebulous matter has been 

 revealed, and there is no reason to suppose that we have yet reached 

 the limit. Illustrations will be given on the screen of successive 

 advances in our knowledge of the nebulas near the Pleiades. 



But, secondly, it seems probable that there are nebulae which are 

 not shining at all, and of which we can only get evidence from their 

 screening or obstructing the light of other bodies. Thus in the 

 picture of the nebula near t, Orionis there are many more stars on 

 one side of the nebulous boundary than on the other. Do the stars 

 really stop at this boundary ? or is it not much more likely that the 

 nebula here chaiiges in character and becomes more obstructive to 

 the light of stars beyond ? 



Again, there are dark patches of the sky apparently devoid of 

 stars. The first thought that occurs to us in seeing one of them is 

 that it is a black hole — ein Loch im Himmel, as Herschel said. But 

 can it really be a gigantic tunnel piercing the whole universe and 

 pointed directly towards us ? Both these conditions are necessary 

 for this explanation. A much simpler idea is that there is some 

 obstructing body — which we may call a dark nebula — comparatively 

 near us, hiding the light from stars beyond. Thus the idea of dark 

 nebulae was already in the minds of astronomers before the discovery 

 of Nova Persei in February 1901, and wc have now to notice a 



