November 8, 1900] 



NA TURE 



31 



space, we find a very great difference in relation to the 

 plane of the Milky Way ; but irrespective of this it may 

 be said that omitting some 500 of the brighter stars, 

 which have to be classed separately, up to the 9th 

 magnitude, the actual and theoretical numbers are 

 fairly accordant, but there is a distinct indication of a 

 thinning out of stars after the gih magnitude is passed. 

 An example of this has been furnished by Prof Pickering, 

 who has given us a very useful diagram of the brightness 

 of the stars seen within r from the celestial pole : that 

 is to say, a region about 28° from the Milky Way. There 

 is a very considerable number of stars of the 9th and 

 loth magnitudes, but very few of the 14th and 15th. In 



fingers by talking about them. If, however, we consider 

 the matter from the point of view at which we have now 

 arrived from the complete discussion which is open 

 to us, the question arises whether this enormous 

 increase of nebulae towards the poles of the Milky Way 



Fig 2. — The great nebjjla in Andromeda, from a photograph by 

 Dr. Roberts. 



that way it is possible to investigate the conditioning of 

 stars with regard to their brilliancy in the Milky Way 

 itself ; the value of the diagram now given is that it shows 

 what happens in a position away from the plane. 



There is one other point which arises which is well 

 worth our attention. It is a subject that we have to 

 approach with caution, because it is such a large one, 

 and because so little is known about it. When we look 

 away from the plane of the Milky Way to the poles, we 

 find, as the late Mr. Waters very conclusively proved 

 to us by his tabulations, the greatest number of so- 

 called nebulas ; it is very difficult to discuss this matter, 

 because the nature of these nebulae is undefined, we 

 are without any information as to whether they are 

 gaseous nebulae or non-gaseous, and we may burn our 



NO. 16 '9, VOL. 63] 



Fig. 3 — The ring nebulae in Lyra. 



does not show us that these things are probably other 

 universes, other systems, like our own. We must con- 

 sider most of the stars which we see with* our most 

 powerful telescopes as belonging to our own system. 

 The number, as we know, increases tremendously as the 

 plane of the Milky Way is approached, and it is possible 

 that as that central plane of the system contains not 

 only stars but nebulae, it must also contain any number 

 of dark bodies down to the smallest meteorite, and that 

 we may possibly have there a vera causa for an ex- 

 tinction of light near the plane of the Milky Way, which 

 is not possible in other parts of the heavens, especially 

 towards the galactic poles. If that be so, the increase of 

 "nebulae" towards the poles of the Milky Way may 

 simply mean that we see other universes than our own 

 in greater plenty where the conditions for seeing them 

 become more favourable, and that is the reason why 

 towards the poles of the Milky Way we have this over- 

 powering number of apparently nebulous bodies. Of 

 course if that be so, what will turn out will be that most,, 

 if not all, of them are not nebulae at all ; they are systems 

 like our own, are clusters of stars with which our own 

 system has absolutely no concern or connection. 



MAG 9 10 



MAG 9 10 II 



12 li •♦ 



Fig. 4. — Pickering's diagram. 



It follows also that the overwhelming number of very 

 faint stars in the Milky W^ay are stars which would appear 

 brighter if they happened to lie near the galactic poles. 



The above suggestion is only an extension of an idea 

 first put forward I believe by Schiaparelli. In spite of 

 the considerable literature on the subject of the extinction 



