Specimen Observations on the Galilee 



35 



x'ariable pai't of the error due to ship's magnetism, but still contains the constant A^ (see 

 p. 78). The value of A^ is determined by comparison of the mean ship value with the mean 

 value resulting from the surrounding shore observations, both referred to the same time on 

 May 25, 1908. Thus the ship value referred to mean of day is + 17?90; the value from the 

 surrounding shore observations, referred to mean of day, is -|-17?88; hence, the value of 

 A^ is +0?02. 



The variable part of the deviation-correction is obtained from Form 23 (Analysis of 

 Declination Deviations, p. 36), First the observed deviations, without Aa, are derived on 

 Form 22, sixth column, by subtracting the mean value D„ of the observed magnetic 

 declination D from the individual values of D. These quantities are then analyzed by 

 means of Form 23, presently explained. Next the computed deviations, derived on Form 

 23, are entered on Form 22 and applied together with A^, reversing signs, to the observed 

 D's (fifth column). Thus finally the entries in last column, "Corrected magnetic declina- 

 tion," are obtained. 



Computatimi of Ocean Declination Observations (Swing) 



(Form 22) 



Stalwn: San Francisco Bay 

 Date: May 25, 1908, A. M. 

 Compass: Ritchie 29499 (R3C) 

 Method: Prism and Alidade 

 Sea: S Weather: b 



Lai: 37° 51' N 

 Vessel: Galilee 

 ObsW: W. J. P. 

 Wind: 

 Roll: 0° 



Long: 122° 23' W 

 Com'd'r: W. J. P. 

 Comp'r: D. C. 8. 

 Reviser: J. P. A. 

 Helm: Port 



Ship's 

 Head 



N 

 NE 



E 

 SE 



S 



sw 

 w 



NW 

 Means 



Local 



Apparent 



Time 



n m s 



5 44 34 



5 55 00 



5 59 10 



6 25 38 

 6 32 05 

 6 38 38 

 5 28 51 

 5 37 44 



Sun by 

 Compass 



N 53.24 E 

 54.62 

 55.30 

 59.00 

 59.44 

 60.14 

 50.69 

 52.16 



N 55.57 E 



Sun's 

 Azimuth 



N70.98E 

 72.46 

 73.06 

 76.76 

 77.66 

 78.58 

 68.73 

 70.02 



N73..53E 



Obs'd 

 Mag. 

 Decl'n 



+ 17.74 

 + 17.84 

 + 17.76 

 + 17.76 

 + 18.22 

 + 18.44 

 + 18.04 

 + 17.86 



+ 17.96 



Deviation 

 (without Ati) 



Obs'd Comp'd 



-0.22 

 -0.12 

 -0.20 

 -0.20 

 +0.26 

 +0.48 

 +0.08 

 -0.10 



0.00 



-0.20 

 -0.15 

 -0.21 

 -0.11 

 +0.24 

 +0.43 

 +0.17 

 -0.17 



0.00 



Corr'd 

 Mag. 

 Decl'n 



+ 17.92 

 + 17.97 

 + 17.95 

 + 17.85 

 + 17.96 

 + 17.99 

 + 17.85 

 + 18.01 



+17.94 



Magnetic dechnation for mean of day from ship observations +17?90 

 Magnetic declination for mean of day from shore observations + 17 . 88 

 Hence, value of A^ + . 02 



It will be seen that while the observed magnetic declinations varied from +17?74 to 

 + 18?44, hence through a range of 0?70, the corrected ones exhibit a range of but 0?16 or 10'. 

 The headings and adjacent designations, together with the explanation made and the 

 formulae at the bottom of the form, will make clear the various steps followed on Form 23 

 (Analysis of Declination Deviations). The observed deviations without At for port helm 

 are taken from specimen Form 22, the starboard-helm results being derived from a similar 

 computation sheet. Next are given the mean results for both helms. Proceeding now to 

 the lower half (II) of the page, the deviation-coefficients B^ = -0?19, Ci= -0?22, 0^ = 

 -f 0?14, and Ei= +0?02, ai-e derived, as indicated in the scheme of computation. Know- 

 ing these coefficients, the computed values of deviation without Aa are obtained in the 

 upper right-hand portion (III) of the form. Finally, the residuals v (observed — computed 

 deviation) are entered, and the values of v\ from which the probable error of a deviation 

 without Ai on a, single heading is derived by the formula at the bottom of the form; it is 

 found to be±0?03 or ±2'. 



