4 SCIENCE PROGRESS 



From an examination of the near stars — which, on the average, 

 are those of large proper motion — Kapteyn concludes, as might 

 be expected, that these are distributed uniformly, and have no 

 connection with the Milky Way. Referring again to the table, 

 it is seen that the stars down to the ninth magnitude are nearly 

 three times as dense in the Milky Way as at the galactic poles, 

 whilst those in Herschel's star gauges are nearly twenty times 

 as dense, this large ratio being due to the fact that the star 

 clouds in the Milky Way contain an immense number of very 

 faint stars. This latter result is apparently contradicted by some 

 recent star-counts made by Messrs. Chapman and Melotte at the 

 Royal Observatory, Greenwich, based upon a series of photo- 

 graphs of the whole sky taken by the late John Franklin-Adams. 

 This investigation indicated that the galactic concentration did 

 not vary greatly over the range s - o m.-17'o m. of photographic 

 magnitudes. An explanation of this discrepancy has been 

 suggested by Prof. H. H. Turner — viz. that the galactic regions 

 may contain a very large number of faint red stars visible 

 in Herschel's telescope, but too red to affect the photographic 

 plate. A similar effect would be caused if, as is more than 

 probable, there is absorbing matter in space, which scatters the 

 light of short wave-length, and makes the distant stars appear 

 reddish, similar to lights seen through a fog, and so incapable 

 of affecting the photographic plate. In any case, however, it 

 is certain that there is a very marked flattening of the system 

 as a whole towards the Milky Way. 



A comparison of any of the above north galactic zones with 

 the corresponding south zones shows that in each case the 

 density in the southern zone is greater than that in the northern ; 

 the explanation of this fact (which is generally accepted) is that 

 our solar system lies somewhat to the north of the galactic 

 plane, and a close study of the course of the Milky Way in the 

 heavens lends support to this view. Struve found that it does 

 not trace out a great circle on the celestial sphere whose centre 

 is our solar system, but a small circle at a distance of about 88° 

 from the south galactic pole. 



Of still greater interest is an examination of the galactic con- 

 centration of stars of different types. It is believed that the 

 stage in its evolution at which a star has arrived can be told 

 with considerable certainty from its spectrum. The classes in 

 the supposed order of evolution are denoted by the letters B, A, 



