ASTRONOMY 



then, the element of distance, we can obtain directly 

 from the photographs information regarding the 

 distribution of the stars in direction. The main 

 point which emerges in this connection is that as we 

 approach the plane of the Milky Way the number 

 of stars which can be counted in an area of given 

 size increases very rapidly, indicating that the 

 stars separately distinguishable as such and the 

 massed legions of the Milky Way form but one 

 system. Until more is known regarding relative 

 distances it is impossible to form an exact idea of 

 the geometrical form of the universe. The work- 

 ing hypothesis which is generally accepted at the 

 present time is that the shape is something like a 

 bun or lens, our sun being near the centre, and 

 that encircling it, perhaps in spiral fashion, are 

 the star-clouds which constitute the Milky Way. 



Another group of problems of a geometrical 

 character are those relating to the motions of the 

 stars. 



The term ' fixed ' as applied to the stars is a 

 misnomer. Its partial justification arises from the 

 fact that the apparent motions are so slow that the 

 changes in position which they produce can only 

 be detected by careful measurements made with 

 accurate instruments at times separated by a con- 

 siderable interval. Halley was the first to detect 

 any motion, and this he did by comparing the 

 observations of his own day with those made by 



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