The Evolution of the Sciences 



due to the fact that the sun occupies no special 

 position in the Milky Way and plays no pre- 

 ponderating part in the motions of the heavens. 

 But if, on the other hand, the sun has a motion 

 of its own, stars moving in the same direction, 

 and at the same speed, will appear at rest 

 relatively to it, while stars moving in the opposite 

 direction will, on the contrary, appear to be 

 moving more rapidly. Thus the mean dis- 

 tribution of stellar velocities with reference 

 to the sun will show a predominant direction 

 which is that of the sun's own movement. 

 In the same way, if one stands still in a crowd 

 moving in all directions, all passers-by approach 

 and recede with equal speed, whatever their 

 direction may be, but if the observer also walks, 

 those who are following the same line will 

 appear to approach more rapidly or to recede 

 more slowly than those who are walking at an 

 angle to his path. 



Such, in principle, is the method applied 

 by Sir W. Herschel, Argelander and Airy. It 

 shows that the sun is travelling with a velocity 

 of nearly twelve kilometres per second towards 

 a point situated at the centre of the constellation 



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