EiAMBAUT — Determining Didcmce of a Double Star. 669 



Then log? = 1-2665 



log a = 0-5821 



log sin (^ - X) = 9-9949 

 log sin y = 9-8469 



1-6904 1-6904 



h p' 



log- =9-9673 log -=0-1249 



h p' 



log/fl5-sin(<^-A) siny= 1-6577 1-8153 = log /a-sin(<j!)-X)siny 



a 



logP = 2-0701 2-0701 



log- =9-8075 log - = 9-9673 



a a 



Pu Ph 



log-^ = l-877t) 2-0374 = log — . 



a a 



.-. lognr =9-7801 9-7779 = log nr. 



UV =0-6026 0-5996 = nr. 



Or, finally, nr= 0-601. 



If it be required to find the time at which IT V attains this value, 

 we have ^ = A.= 327°15', and from equations (1) and (2) we can 

 find t. I have added below the values of k for a number of stars the 

 elements of whose orbits are taken chiefly from Houzeau's Vade Mecum. 

 I would draw attention to the results in the cases of Sirius and a Cen- 

 tauri, for which k is found to be 5-40 and 6-02 respectively. Now these 

 numbers, even if we had had no knowledge otherwise of their paral- 

 laxes, would have pointed to these stars as being wdthin measurable 

 distance, and seem to show that in the case of a Centauri spectroscopic 

 observations might have been employed in the year 1879 to test the 

 measures of parallax made up to that time, since from these figures, 

 taking its parallax, as determined by Gill and Elkin, as 0"-75, it must 

 have been moving in the line of sight with a velocity of eight miles 

 per second in April of that year. In the case of Sirius, although the 

 value I have found for h, taken in conjunction with the value 0"-4 for 

 its parallax, would show that in September, 1890, the companion will 

 be moving with a velocity of thirteen miles per second in the line of 

 sight, the great difference in the magnitudes of the components 

 would, I fear, preclude the possibility of applying the spectroscopic 

 test. 



Out of this list of thirty -nine stars there are five for which the value 

 of n Fexceeds unity, namely, -q Cassiopese, a Canis Majoris, a Centauri, 

 70 jy Ophiuchi, and y Coronae Australia; and of these five no less than 



