The Milky Way 



Hercules, in the northern hemisphere . This point 

 was called by Herschel the apex, because the sun, 

 while moving towards it, rises in the heavens. 



Now that the proper motion of the sun has 

 been defined the same can be done for every 

 star whose relative motion, referred to the 

 sun, is known. Each star is found to have an 

 apex of its own, towards which it travels with- 

 out intermission, each at its own velocity; 

 the velocity of Aldebaran, one of the highest 

 determined, reaching 48 kilometres per second. 

 The brightest stars in the sky travel at an 

 average velocity of 25 kilometres per second; 

 the sun must therefore be classed among the 

 stars of slow displacement. The question arises, 

 What is the law of all these displacements? Is it 

 so complicated that its effects are apparently 

 those of chance? The necessary facts for a solu- 

 tion of this important problem are not yet avail- 

 able, but a very original hypothesis of Madler, 

 a Dorpat astronomer, is worth mentioning. 

 Madler remarks that all systems, subject to 

 the law of universal gravitation, are animated 

 by a movement of rotation round a centre. 

 This centre need not necessarily be a material 



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