94 Ocean Magnetic Observations, 1905-16 



quantities resulting from the observations with all instruments used for any particular 

 element are given. The letters E and W serve to indicate whether the magnetic decUnation 

 is east or west of north. The letters A'' and -S show whether the north-seeking end of the 

 magnetic needle points below the horizon, as it does in the northern magnetic hemisphere, 

 or above, as it does in the southern magnetic hemisphere. 



The ocean values of horizontal intensity, derived as explained on pages 23-26 with all 

 instruments employed, are tabulated to the fourth decimal of the c. g. s. unit of magnetic 

 field-intensity. In magnetic-survey work on land the fourth decimal is often uncertain by 

 one or more units, and in ocean work the error may approach a unit in the third decimal 

 place. It is thus to be understood that no claim is made for the correctness of the last 

 figure; it has been retained here primarily in order that when all reductions to common 

 epoch' have been appUed on account of the various magnetic variations, the error (due 

 purely to computation) will be kept down to the desired limit. 



The question whether to give values of the horizontal intensity exclusively, or values of 

 total intensity, was decided in the previous volumes, for reasons there stated, in favor of 



the former. ^^ . ^ ,, 



The instruments used are shown in the columns "Compass" and Dip Circle. The 

 designations of the various instruments employed will be found stated on pages 28-32. 

 The term "Compass" also includes the "Sea Deflector," with which both declinations and 

 horizontal intensities were observed, as described on pages 17-19. The term "Dip Circle" 

 likewise includes the "Sea Dip-Circle" when used for determination of the total intensity 

 from which the horizontal intensity is derived, as explained on page 23. The designation 

 169.1234, for example, means that dip circle 169 was used, the inclination being observed 

 wdth regular dip needles 1 and 2, and with deflected needle 3, and that the total intensity 

 was observed with the same instrument by the deflection method, using the intensity 

 needles 3 and 4 (the ones itaMcized). Similarly 189.9,10,75 means that inclination was 

 observed with dip circle 189, using regular dip needles 9 and 10, and deflected needle 7, 

 and that, furthermore, total intensity was obtained by the deflection method, using inten- 

 sity needles 7 and 8. Invariably the intensity needles are italicized and are given last. 

 The higher number of the two intensity needles always designates the chief intensity needle 

 (the deflecting and the loaded needle). Whenever the total intensity was determined 

 from both loaded-dip observations and deflections, this fact is shown by the addition of the 

 dagger (f) ; thus, e. g., 169.123.4t, or 189.9,10,7<St, as the case may be. When, as had to be 

 the case with sea dip-cu-cle 169 on a portion of the Galilee's first cruise (see p. 19), 

 total intensity was obtained only with the loaded needle (No. 4), and the inclination was 

 observed with the regular dip needles (Nos. 1 and 2), then the designation is 169.12^. By 

 turning to the method of observations, pages 17-26, and 33-58, any additional explanation 

 may be obtained. (See also inventory of instruments used aboard the Galilee, pp. 28-32). 

 The columns of "Remarks" contain: 



a. Course. This is the ship's magnetic course (heading) on which the observations were 

 made. When the word "swing" occurs this means that the vessel was swung durnig 

 observations. A harbor-swing of vessel imphes that the vessel was swung on at 

 least 8 equidistant headings with both port and starboard helms. The swings 

 at sea with a sailing vessel could rarely be complete, the aim, however, being, in 

 general, to secure 8 equidistant headings; not infrequently one, two, or even 

 three out of the desired 8 equidistant headings would be missed. For all swings, 

 the local mean times given in the respective columns denote the times of beginning 

 and ending of the swing. The deviation-coefficients and details regarding swmgs 

 will be found in Tables 23 to 28, pages 81-85. 



In the case of the Carnegie, because of the absence of deviation-corrections, 

 it was also possible to make observations when the vessel's heading was shifting, 

 as would be the case when the vessel was "becalmed," or "at anchor." 



