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PROFESSOR A. S. EDDINGTON, F.R.S., ON 



the same way ; but, as a matter of averages, there is a large 

 preponderance of arrows in a particular direction. This general 

 motion of the stars is a most conspicuous phenomenon. The 

 first man who detected it was Sir William Herschel, and, 

 although at that time he had only seven stars of known motion 

 to work with, he detected even in those few stars the systematic 

 movement, and (no doubt rather luckily) he pointed out quite 

 closely the point towards which the motion was directed. 



At first sight this seems a remarkable bond between the 

 stars, widely scattered as they are ; but a little consideration 

 shows that it is illusory. When you are in a train, waiting at a 

 station with another train alongside, if one train starts it is 

 often difficult to tell whether it is your own train or the other 

 that is moving. Tor some reason, I believe, there is a tendency 

 to guess wrong ; you think it is the other train moving back- 

 wards when it is really your own train moving forwards. Now, 

 in the stellar universe we are in an even worse position : not 

 only is it impossible to tell whether the effect which we see is 

 really the whole system of the stars moving towards Canis 

 Major, or our own sun, carrying the earth with it, moving in 

 the opposite direction towards Lyra — not only is it impossible 

 to find out which of these is taking place, but even the distinc- 

 tion between the two ideas disappears. Eelative to the sun, 

 the stars are moving towards Canis Major ; relative to the stars, 

 the sun is moving towards Lyra — either phrase expresses the 

 same fact, and it is impossible to go behind it and say which, 

 if either, is at rest. 



But the point of immediate importance is that, if the whole 

 effect can be attributed to a motion of the sun, it clearly cannot 

 imply any particular bond among the stars. To find any trace 

 of organization we must look further, and, making allowance 

 for this solar motion, as it is called, see if the residual move- 

 ments of the stars show any peculiarities, or if they are hap- 

 hazard. 



It was in 1904-5 that Professor J. C. Kapteyn, of Groningen, 

 first examined this question thoroughly and showed that the 

 stars are not moving in a haphazard way. He arrived at the 

 startling result that the stars form two great streams moving 

 through one another. What an amazing conception this is ! 

 I have tried to show the enormous scale of the universe 

 of stars ; and now we find that they are ordered in two mighty 

 streams. If you will follow me through a somewhat elaborate 

 argument I will show how these two streams manifest them- 

 selves. 



