1014] on The Stars around the North Pole 185 



Although there is fair agreement for the stars of smallest luminosity, 

 there is an increasing divergence between the results for those of higher 

 luminosity. Xow, it is to be remembered that these figures have been 

 derived from regions at different distances from the sun. Thus the 

 stars which are between 16 and 40 times the brightness of the sun, 

 and which are apparently of magnitude 10 to 11, lie between 398 and 

 631 parsecs, while those which are apparently of magnitude 9 to 10 

 lie between 251 and 398 parsecs. We may conclude therefore that 

 the density of this class of stars is somewhat less at this greater dis- 

 tance from the sun. Following out this line of reasoning, the 

 diminution of density of the stars is' found to be as follows : — 



At 50 parsecs 



„ 100 „ ... 



„ 200 ,, ... 



„ 300 „ ... 



„ 400 „ ... 



„ 500 „ ... 



Although much weight cannot be attached to the exact figures, 

 there must be, I believe, a very considerable falling off in the density 

 of the stars between the distances of 100 and 500 parsecs. A falling 

 off in the total density of the stars would affect the tables, giving the 

 proportion of stars of different brightness, and would increase con- 

 siderably the proportion of bright stars. 



25. Although the conclusions presented in this discourse have 

 been derived from a study of the proper motions of the stars in a small 

 area of the sky, and may be somewhat modified by the investigation 

 of other regions, they may be considered as fairly applicable to the 

 stars in general. We have considered the stars down to a magnitude 

 approaching 11-0. There are in the whole sky half a million stars 

 brighter than this limit of magnitude. 



We may say of them — 



(1) On the whole, the yellow stars, the stars like the sun in 

 physical condition, are the nearest. 



' (2) They lie within fairly narrow limits of distance — 80 per cent 

 are between 100 and 500 parsecs ; 10 per cent nearer than 100 parsecs ; 

 and 10 per cent farther away than 500 parsecs. 



(3) As we go from the yellow to the blue or the orange stars, the 

 average distances increase. 



(4) The red stars are at great distances — an average of about 

 1000 parsecs. 



(5) The stars vary greatly in intrinsic brightness. The red stars 

 are specially luminous, being on the average 100 times as bright as 

 the sun. 



(6) If we consider all the stars down to this limit of magnitude, 

 we find that approximately 95 per cent are intrinsically more luminous 

 than the sun. 



