58 LIGHT SCIENCE FOR LEISURE HOURS. 



and the inconceivable activity really present there. It 

 seems incredible that all those orbs which look so still 

 are speeding through space with a velocity compared 

 with which every form of motion familiar to us on 

 earth must be regarded as almost absolute rest. This 

 appears even more surprising when we consider that 

 during all those centuries with which history deals, 

 during the rise and fall of the nations of antiquity, 

 during the darkness of the Middle Ages, during the 

 more familiar scenes of recent centuries, the stars 

 have presented an aspect so constant that if the Chal- 

 dsean astronomers could be restored to life, they would 

 recognise scarce any change in the positions of the stars 

 forming the ancient constellations. Yet there are no 

 astronomical facts more thoroughly established than 

 those which relate to the motions of the stars. The 

 giant orb of Sirius, exceeding our sun a thousand times 

 in volume, Capella and Procyon, the glories of Orion, 

 the clustered Pleiads, Arcturus, Vega, and Aldebaran, 

 all the stars known to the astronomer, are urging their 

 way with inconceivable velocity, each on its own course, 

 though doubtless all these motions are subordinated to 

 some as yet unexplained system of movements whereby 

 all the stars of the galaxy are made to form parts of 

 one harmonious whole. 



Until lately it had only been by one method of 

 observation that the astronomer could assure himself 

 that these motions were taking place. That method is 

 the simplest conceivable. If a star s place were accu 

 rately determined, either with respect to neighbouring 



