MoNCK — On Star-Distribution. 495 



average distance of the stars of any given magnitude is greater than 

 the average distance of the stars of the magnitude next above it. 

 Nearness and remoteness in the case of the fixed stars must be deter- 

 mined on a different scale from that which we employ in dealing with 

 the solar system. The nearest of them is much more remote than 

 Neptune ; but it is not improbable that there are stars within the 

 range of our telescopes whose distance exceeds that of a Oentauri 

 more than a thousandfold. Any star whose distance does not ex- 

 ceed ten times that of a Oentauri must be regarded as a near star. 

 On the hypothesis of uniformity there would be one thousand such 

 stars, and the actual number is as likely to exceed one thousand 

 sa to fall short of it. But, taking the annual parallax of a 

 Oentauri at -f^ of a second, the annual parallax of a star ten times 

 as distant would be only -j^-^- of a second ; and I think it will be 

 admitted that such a parallax could not be measured by our pre- 

 sent methods and with our present instruments with any approach 

 to accuracy. That we have, tried to find a parallax for any given 

 star and have failed is therefore no proof that it is not a near star. 

 In fact, the number of stars which are universally admitted to have 

 a sensible parallax might almost be counted on one's fingers. But, 

 to revert to the parallax of stars of the first magnitude, I turn 

 again to Dr. Ball's Elements of Astronomy, which contains a valu- 

 able collection of facts which are quite sufficient for my present 

 purpose. Beside a Oentauri I find a very fair concurrence by 

 different observers in the case of Sirius, the parallax of which can 

 hardly be less than i of a second. Two measures only are given 

 of the parallax of Arcturus, but they agree in fixing it at between 

 4- and -^ of a second. The more recent determinations of the paral- 

 lax of Wega are also in fair agreement, and give a result larger 

 than in the case of Arcturus, and perhaps equal to Sirius. There 

 is therefore, I think, good reason to conclude that four stars of the 

 first magnitude possess a sensible parallax ; and, judging from 

 Dr. Ball's figures, there are at least four more with regard to 

 which further investigation may not improbably lead to the same 

 conclusion, though the present data are either too insufficient or 

 too discordant to afford any positive result. These are /3 Oentauri, 

 Al Tair, Capella and Procyon. If I am right in these conclusions, 

 20 per cent, of the stars of the first magnitude have a sensible 

 parallax, and further research may not improbably increase this 



SCIEN. PEOC. R.D.S. — VOL. IV. PT. IX. ■ 2 U 



