314 DISCUSSIONS IN COSMOLOGY. 



before we could be certain whether it was changing its 

 position or not. And even after we had found with 

 certainty that the star was shifting, and this at the rate 

 of 1 ' in 1800 years, we could not, without a knowledge 

 of its distance, express the angle of displacement in 

 miles. But from the apparent magnitude or brilliancy 

 of the star, we could not determine whether its distance 

 was 10 times, 100 times, or 1000 times that of 

 a Centauri; and consequently we could form no conjec- 

 ture as to the actual velocity of the star. If we assumed 

 its distance to be 10 times that of a Centauri, this 

 would give a transverse velocity of one mile per second. 

 If we assumed its distance to be 100 times that of 

 a Centauri, this would give 10 miles a second as the 

 velocity, and if 1000 times, the velocity of course would 

 be 100 miles per second. 



As there are but few of the stars which show a 

 measurable parallax, and we have no other reliable 

 method of estimating their distances, * it follows that 

 in reference to the greater number of the stars, neither 

 by spectrum-analysis nor by observation of their change 

 of position can we determine their velocities. There 

 does not, therefore, appear to be the shadow of a reason 

 for believing that none of the stars has a motion of 

 over 30 or 40 miles per second : for any thing that 

 at present is known to the contrary, many of them may 

 possess a proper motion enormously greater than that. 



There is, however, an important point which seems 

 to be overlooked in this objection, viz., that, unless 

 the greater part of the motion of translation be trans- 

 formed into heat, the chances are that no sun star will 

 be formed. It is necessary to the formation of a sun 



* It is true that we may one day be able to determine by spectrum - 

 analysis the distance of some of the binary stars ; but as yet this 

 method has not been applied with success. 



