498 Scientific Proceedings, Royal Dublin Society. 



cannot suppose such double stars to be very distant from us with- 

 out ascribing an almost incredible velocity to the revolving star. 

 It is otherwise, of course, when the double star is a very close one, 

 or when the period of revolution is very long. But, I believe that 

 duplicity of any kind occurs more frequently in the case of the 

 brighter than of the fainter stars, and that the average distance of 

 the pairs is also greater in the former case than in the latter. 

 This is exactly what we should expect to find if the brighter stars 

 were nearer. In speaking of double stars, I exclude cases in which 

 the two stars are not known to have any physical connexion, and, 

 though nearly in the same direction, may be at very different dis- 

 tances from us. Excluding these stars, I believe the feature on 

 which I am insisting will be much more frequently found among 

 the brighter than the fainter stars, though I am unable to give any 

 statistics as to the proportion. 



My next reason is founded on what I may call star-systems — 

 stars fairly separated from each other, yet moving in nearly the 

 same direction and with nearly the same velocity. Such, for in- 

 stance, is the case with five of the seven stars which form the 

 Plough, or Charles's Wain, in the Great Bear. They are all 

 bright stars, but probably further examination will show that some 

 faint stars in the same direction are also members of the system. 

 Now, considering the great angular distances of these stars from 

 each other, their mutual action would be almost inconceivable if 

 they were not near stars in the sense in which I have been using 

 that phrase. I think I may go a step farther. This system ap- 

 pears to be sweeping through space uninfluenced by the action of 

 the numerous fainter stars which we see around it ; for if it once 

 got entangled in a mass of stars moving in different directions and 

 with different velocities, it is difficult to see how the common mo- 

 tion of the system could be preserved. The natural inference 

 therefore is, that these faint stars are much more distant from us 

 than this system of five — that, great as the mutual distances of the 

 members of that system must be on the lowest computation, the 

 distance of the system from the general mass of the stars in the 

 Great Bear is still greater. A somewhat similar system exists in 

 Cassiopeia's Chair, embracing most of the brighter stars in that 

 region. The angular distance of its members is less than in the 

 Great Bear, but the component stars are also less brilliant — the 



