14 Ocean Magnetic Observations, 1905-16 



almost a direct one to about 31° north latitude in 137?5 west longitude, from which point 

 course was set for the Golden Gate. San Francisco was reached on May 21, 1908, thus 

 concluding Cmise III, begun at San Diego on December 22, 1906, and having a total length 

 of about 36,977 nautical miles. 



On Cruise III, 12 harbors were visited, at all of which extensive shore observations 

 and intercomparisons of ship and land instruments were made ; in 3 of the harbors swinging 

 ship could not be undertaken, either for want of tug facilities or because of insufficient 

 space. 20 primary land stations were established ; also, in the neighborhood of the primary 

 stations, 20 secondary stations for purposes of intercomparison and standardization of ship's 

 instruments. While at sea during Cruise III, in addition to the course observations, which 

 were made as frequently as weather and sea conditions permitted, frequent swings, under 

 sail, on 6 to 8 headings, were carried out. Astronomical observations for position, with 

 determinations of position by dead reckoning, daily intercomparisons of 5 chronometers, and 

 daily meteorological observations were made. 



The closing shore observations were made at San Francisco, and after the swing obser- 

 vations on May 23, 25, and 28 were completed, the Galilee was returned to her owners on 

 June 5, 1908. She had been in almost continuous commission since August 1905, or a 

 period of 3 years less 2 months, during which cruises of 63,834 nautical miles were carried 

 out with her in all parts of the Pacific Ocean, without serious mishap, and without loss of 

 human life. For further information regarding Cruise III, the abstract of ship's log 

 (pp. 147-154) may be consulted. The three cruises of the Galilee are shown on Plate 6. 



METHODS OF WORK ON THE GALILEE. 



GENERAL PRINCIPLES FOLLOWED. 



From the very beginning of the ocean magnetic work on the Galilee in 1905, two princi- 

 ples were steadfastly held in \'iew: 



a. To get useful work done and make the results promptly known. 



b. To strive for the highest accuracy attainable in all magnetic elements. 



Early in 1905 the Director spent a month abroad consulting various eminent investi- 

 gators as to the requirements of ocean work, but could get practically no information 

 in addition to what he had already obtained in his previous experience on Coast and 

 Geodetic Survey vessels, on board of which magnetic work had been initiated under his 

 direction in 1903. Thanks to this experience, it was possible for him, during the period of 

 the experimental trip of the Galilee from San Francisco to San Diego, in August 1905, to fix 

 upon the methods used practically throughout the three years the vessel was in commission. 



The general principles followed were to secure complete control of each instrumental 

 constant in every available manner, and to obtain independent checks upon the observed 

 values of the magnetic elements by securing simultaneouslj^ two independent determina- 

 tions of each element, under conditions as widely different as possible; i. e., different 

 observers, different instruments, and at different stations on the observing bridge, so that 

 the corresponding ship-corrections or deviation-corrections would either vary in amount 

 or even change sign. 



The instructions called for special harbor swings when feasible, each swing to be on both 

 helms and on a separate day. These swings generally required a tug, though a launch would 

 do under favorable weather conditions. Swings at sea, under sail, were also prescribed at as 

 frequent intervals as conditions of sea and weather permitted. Under sail, usually one and 

 sometimes two out of eight equidistant headings would be missed. In order to make 

 swings possible for a saihng vessel in calm weather, the Galilee was equipped on her second 

 cruise with a naphtha launch swung at the stern davits when not in use. With the aid of 



