140 



Ocean Magnetic Observations, 1905-16 



The linear displacement due to 2n = 2 (z + w) , was measured on board ship by a 

 scale held against the peep-sight and was found to be 4.75 mm. The distance between 

 the mirror and peep-sight is 226 mm., and since the image of the peep-sight was deflected 

 to the apparent right, 



4 75 



tan 2n = tan 2{z-\- w) = — 



226 



or n = - 0?60 



The sign was verified by actual experiment. Using a small sextant mirror, it was 

 found that if it was turned so as to deflect the peep-sight image to the right the bearings 

 were too large (clockwise). 



The values of y, z, and w as finally determined from a least-square adjustment of all 

 observations made with this instrument, are the respective numerical coefficients in the 

 following equation : 



Aac- Xo = - 1?682 tan h - 1?173 tan /i tan^ + 1?750 tan h sec ^ 



The observed values of Aac, h, and the weights p assigned in the above-mentioned 

 least-square adjustment are tabulated below, together with the differences between the 

 observed values of Aac and those obtained by computation from the derived formula. 

 These differences are given in the column headed — C. 



Table 41. — Portion of Alidade Corrections for Standard Compass RSC Dependent on Altitude. 



No. 



Station 



San Diego 



Do 



Papeete, Tahiti 



Do 



Do 



Do 



Yap 



Do 



Do 



Woosung 



Do 



Do 



Do 



Sitka 



Do 



Do 



Do 



Honolulu 



Do 



Do 



Jaluit 



Christchurch . . 



Do 



Do 



Callao 



San Francisco. 



Date 



1906 

 Dec. 14 

 Dec. 15 



1907 

 Feb. 9 

 Feb. 9 

 Feb. 12 

 Feb. 12 

 Apr. 16 

 Apr. 17 

 Apr. 17 

 May 20 

 May 20 

 May 25 

 May 25 

 July 20 

 July 20 

 July 20 

 July 20 

 Sept. 6 

 Sept. 7 

 Sept. 7 

 Oct. 29 



1908 

 Jan. 4 

 Jan. 4 

 Jan. 4 

 Mar. 17 

 May 20 



Sun's 

 alt. (h) 



33 

 9 



55 

 64 

 36 

 24 

 16 

 52 

 23 

 17 

 51 

 32 

 9 

 50 

 47 

 23 

 16 

 14 

 11 

 44 

 10 



63 

 44 

 21 

 34 

 10 



(Aae-Xo) 



Obs'd 



-0.11 

 +0.06 



-0.45 

 -0.99 

 -0.23 

 -0.11 

 -0.08 

 -0.45 

 -0.14 

 -0.03 

 -0.43 

 -0.17 

 -0.03 

 -0.35 

 -0.23 

 +0 . 03 

 -0.01 

 -0.04 

 +0.03 

 -0.19 

 +0.02 



-0.57 

 -0.38 

 +0.13 

 -0.05 

 +0.02 



Comp'd 



-0.13 

 0.00 



-0 46 

 -0.72 

 -0.16 

 -0.06 

 -0.02 

 -0.39 

 -0.06 

 -0.03 

 -0.37 

 -0.12 



0.00 

 -0.36 

 -0.31 

 -0 06 

 -0.02 

 -0.02 

 -0.01 

 -0.26 



0.00 



-0.08 

 -0.26 

 -0.05 

 -0.14 

 0.00 



0-C 



+0.02 

 +0.06 



+0.01 

 -0.27 

 -0.07 

 -0.05 

 -0.06 

 -0.06 

 -0.08 

 0.00 

 -0.06 

 -0.05 

 -0.03 

 +0.01 

 +0.08 

 +0.09 

 +0.01 

 -0.02 

 +0.04 

 +0.07 

 +0.02 



+0.11 

 -0.12 

 +0.18 

 +0.09 

 +0.02 



