﻿46 



Mr. A. S. Davis on the Probable 



in which it is seen may be ascertained. Dividing the proper 

 motion by the parallax, this component is obtained expressed in 

 terms of the radii of the earth's orbit per annum. 



The following Table exhibits the components of the velocities 

 thus calculated of the stars which are believed to have a sen* 

 sible parallax. 



Star. 



Parallax. 



Propermotion. 



Component of 

 velocity. 



aCentauri 



0-9187 



0-5638 



0-2709 



0247 



0*226 



016 



0155 



0150 



0133 



0127 



0067 



0046 



3-9 

 512 



6-97 

 0-25 

 0-33 

 1-34 

 0-54 

 2-22 

 003 

 0-44 



4-2 

 91 



30-3 

 1-6 

 21 

 90 

 41 



171 

 2-3 

 96 



61 Cygni 



21250 Lalande 



17415 (Eltzen 



0830Groombridge... 

 70 0phiuchi 



a Lyrae 



Sirius 



iUrsae Majoris 



Arcturus' 



Polaris 



Capella ; 





The average of these velocities is much higher than the greatest 

 value we assumed for the whole velocities of comets at a great dis- 

 tance. It must, however, be noticed that many of these stars 

 were selected as likely to exhibit a sensible parallax because of 

 their large proper motions, and therefore that their average velo- 

 city cannot be taken altogether as an index of the average velocity 

 of all stars. 



IV. More than 300 stars are catalogued as having proper mo- 

 tions greater than 0"*5. If we assume, what will certainly be 

 the fact, that most of these stars have parallaxes much less than 

 /;, 2, then most of them have proper motions much greater 

 than 2-5. 



V. By the displacement of the lines in the spectrum of the 

 light of Sirius, it has been found that it is approaching the sun 

 with a velocity of 29*4 miles a second. This is a velocity of 10" 14 

 radii of the earth's orbit per annum. 



For these reasons we may I think conclude that the velocities 

 of the stars, and therefore of comets, when at a great distance 

 from the sun, are on the average greater than the velocities which 

 we have assumed comets to have in our calculations, and, there- 

 fore, that the percentage of hyperbolic comets having excentrici- 

 ties greater than 1*02 resulting from our calculations will be less 

 than the actual percentage. 



We have hitherto only considered those comets which approach 

 the sun in hyperbolic orbits. It is, however, quite possible that 

 comets may approach the sun for the first time, coming from the 





