Specimen Observations on the Galilee 43 



heading N, is +62?45; applying the correction — 0?08, gives for / corrected, +62?37. 

 The values of 7, corrected in this manner, are entered on the form. The deflection angle u 

 is taken directly from Form 12a, as well as the local mean time and temperature, for each 

 heading of the vessel. The value of the constant C^ is derived from the table of instru- 

 mental constants, and is referred to the date and temperature of the observation-set 

 (see p. 70). With these explanations, the computation of H will be readily followed. 

 Since the angular quantities are expressed in degrees and hundredths, a book of logarithms 

 such as the one mentioned on page 38 will be found convenient. 



Having derived the observed values of H from the deflection-observations, the mean 

 value (0.2500) is taken, and the observed deviations (without A',,) are found; these devia- 

 tions are then analyzed as shown by Form 23a, page 39. The analysis gave for the deviation- 

 coefl^cients, expressed in c. G. s. units: B\= -0.0024; C'h= -0.0056; D\ = -0.0004; and 

 £/'a = 0.0000. With the aid of these the computed deviations (without A\) are obtained; 

 the probable error of the deviation of a single heading is ± 0.0005. The mean observed 

 value of H is 0.2500; since the corresponding value, at the time, as derived from shore 

 observations, was 0.2524, the value of A\= —0.0024. Applying the computed deviations 

 and A\, with reversed signs, to the observed values of H, the corrected values are found. 

 It will be seen that whereas the observed values varied from 0.2440 to 0.2563, hence, showed 

 a range of 0.0123, the corrected values vary from 0.2516 to 0.2531, and exhibit a range 

 of but 0.0015. 



The lower half of Form 25o, the portion marked II, shows the computation of hori- 

 zontal intensity, based on the loaded-dip observations made on the starboard-helm swing. 

 Specimens of these observations for two headings are given on Fonn 11a, page 41. In the 

 formula, / is the corrected observed inclination, as above explained; I' is the observed 

 incUnation with loaded needle 4; u is the angle I — I'. The computation will be readily 

 followed. The mean observed H is 0.2514. The observed deviations are next analyzed, 

 the resulting values of the deviation-coefficients, expressed in c. G. s. units, being : B'\ = 

 -0.0005; C",= -0.0126; £)", = +0.0016; E"i,= +0.0003. The probable error of an 

 observed deviation is ±0.0010, which is somewhat high. The value of A"h is —0.0010. 

 Applying the computed deviations and A",,, with reversed signs, the corrected values of 

 H are obtained, which are seen to exhibit a range of 0.0033, or more than twice that found 

 in the preceding paragraph. The superiority of the deflection observations over the loaded- 

 dip observations in sea work is thus shown. 



Inclination Observations, San Francisco Bay, May 28, 1908. 



On page 44, Form 10a, are specimen inclination-observations with sea dip-cu-cle 189, 

 needle No. 5, .4 end down. These observations are on the two headings N and NE port 

 helm, of the swing in San Francisco Bay, May 28, 1908. As the main object of the swing 

 was to determine the deviations, the polarity of the needle was not reversed, but a corre- 

 sponding correction was applied to detennine the final value of the inclination. The com- 

 plete headings of tliis form, 10a, and its similarity to the total-intensity forms already 

 described, make further explanations unnecessary. 



Passing next to the incUnation values derived from the deflection observations (Form 

 12a, p. 40) with sea dip-circle 189, on May 25, 1908, deviations (without A,) are entered on 

 Fomi 23b, page 45, and analyzed as already explained for the other magnetic elements. 

 The quantities in the second column are derived by applying to the first-derived values 

 (see specimen observations, Form 12a, p. 40) the correction (-0?08) on account of reduc- 

 tion to standard (see p. 69). The mean observed incUnation (7„) is -|-62?30. The plus sign 

 signifies that the north-seeking end of the needle points below the horizon. Subtracting 

 /_, from the individual values of /, the observed deviations (without A,) are obtained. 



