LONGITUDE OF McGILL OBSEEVATOEY. 



143 



The time equations for this date are : 



Group. 



I. 



II. 



III. 



— 16.0 

 + 19.7 

 + 57.1 



For Cirule East. 



0= + 12-2i< + 0.90a + 1.05c + ^T 

 0= + 12.74 + 0.40a + l.OHc + A?' 

 0= + 13.25 — 0.51a + 1.91c + AT" 



For Circle West. 



— 19.2 j = + 12.'SG + 0.89a — 1.04c + ^T 

 + 11.0 ' = + 13.24 + 0.52a —1.03c + AT 

 + 57.0 ■ = + 14. 40—0. 54a — 1.93c + A7' 



Substituting c = + 0'.25 and a = + 0".8*7 in these equations we have, neglecting weights : 



For Circle East. 



From Group I Ar= + 13.29 



From Group II AT = + 13.35 



From Group III AT= + 13.28 



For Circle West. 



s. 



From Group I A 7= + 13.37 



From Group II Ar= + 13.43 



From Group m ^T= + 13.45 



and the mean value JT= + 18*. 362. 



In a solution by the process of least squares, that value of z/T must be used, which 

 results from the solution of the normal equations, but when the solution is made in the 

 form illustrated by this example, it is proper to obtain the value of JT by the combination 

 of only those stars in which the effect of an error iu the azimuth is the most completely 

 eliminated. Stars having a large south declination were observed solely for the better 

 determination of the instrumental constants. Having served this purpose, their further 

 use may properly be dispensed with. 



Making the combination indicated, we have : 



For Circle East. 

 Time. rf A 7' 



h. o 



12.9 + U.G + 13.37 



13.1 + 28.5 • + 13.41 



13.8 + 19.0 + 13.29 

 16.6 + .39.1 + 13.39 



16.9 + 9.5 + 13.33 

 17.1 + 14.5 + 13.39 

 12.8 + .56.6 + 13.28 



13.7 

 14.0 



+ 49.9 

 + 64.9 



+ 13.29 

 + 13.26 



