LONGITUDE OF McGILL OBSERVATOEY. 167 



The greatest diîscordance.s among the values of the unknown quantities derived 

 from the different solutions occur on June 23. On this date, however, the value of 

 the collimation was most carefullj' determined before the commencement of the obser- 

 vations, and soon after sunrise the next morning, by reversal upon a ring of small 

 diameter placed at the focus of a long collimator. Within the limits :^ 0'.04 there 

 can be no doubt Avliatever with regard to the value of this constant for the times at 

 which the observations were made. Assuming that the value of c first determined 

 remained constant until reversal, and that the morning value held true for the entire 

 time after reversal, we have — 



For l;iinii east c = —0.07 

 F(ji- \am[> west c — —0.07 



The equations between (( and c are — 



Fur L:iiii]i East. Vur I.nnip Wi'st. 



>. s. 



For c = -0.07 ,. For e = -0.07 



= +0.11 +0.47« — c a = — 0.3« = —0.72 —1.31.' — r <i = -0.50 



-0.20 — 1.00« +c ^0.-27 —0.43 — 1.08« —c —0.33 



+0.17 +0.53a —c —0.45 —0.49 — 1.0G« — c —0.40 



—0.33 -1.05a +c -0.38 — 0.3'J -1.00(f -c —0.32 



—0.21 -0.92« +r —0.30 



Mean = -0.36 Jlean = -0.3!» 



For the determination of c from the observations for lamp east only, we have — 



s. 



From obseivations above pole, = —0.25 —O.'MUi +c 

 From observations below pole, ~ +0.14 +0.50(' — c 



"Whence, a = —0.22 c = +0.03 



Combining the equations for lamp east and lamp west, we have — 



For the Upper Culiniimtioii. I'or the Lowei' (/iiliniiiatiun. 



Lamp East. = -0.25 — 0.9;)« +c = +0.14 +0.50rt —c 



Lamp West. = — 0.51 —1.11a — c = — 0.51 —1.11a — c 



s. ,s. -s- .V. 



a = —0.36 c = —0.11 a = —0.40 c = -0.00 



It will be seen that the mean of the values for a and c are nearly identical with 

 the values found by the least square solution, while the value of c differs but little 

 from the value found by the mechanical determination. 



With c = — 0-'.07 and a = — 0\.36, the values of AT become — 



F"or lamp east aT = +(;.875 



For lamp west = +G.805 



Mean — +C.885 



