PROBLEMS OF MODERN SCIENCE 



which astronomers are working at the present 

 day. 



At first sight the proper motions of the stars 

 in any small region of the sky would appear to be 

 entirely haphazard and irregular both in direction 

 and in magnitude. But if average values be taken 



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Fig. i. Proper Motions of Stars in Zone 24-32 N. 



a regularity discloses itself. Figure i shows the 

 average proper motions of the stars lying in a 

 narrow zone of the sky whose central line runs 

 2 8 north of the Celestial Equator. The stars 

 in every 2 hours of right ascension, which corre- 

 sponds to 30 of longitude on the earth, have been 

 grouped together. The diagram shows that the 

 stars seem to be flying towards a point south of the 

 zone, situated about 6 h , and away from a point 

 north of the zone about i8 h . If these lines were 

 54 



