Instructions for the Galilee Work 127 



3. Make sea-deflector observations for determining intensity constants (lubber-line on 8 points). 



4. Especial care should be taken with the shore observations, varying the conditions as far as 

 feasible, making them in sufficient number to insure good determinations, and distributing them so 

 as to eliminate, as far as possible, diurnal-variation corrections. When it is necessary to occupy 

 two stations, some tests should be made to insure that there is no appreciable difference in the 

 values of the magnetic elements at the two stations. Full descriptions of land stations must be 

 given. Even if an old station is reoccupied some statement should be made as to surroundings, etc. 

 Notes as to geological formation are specially desired. Observers should remember that the office 

 computer has no knowledge as to the conditions under which observations were made. When 

 intercomparisons are made with other instruments, full record should be made as to methods used 

 and of instruments compared with. In intercomparisons with observatory instruments, stations 

 should hkewise be exchanged, unless the local observer deems the exchange unnecessary. 



5. Prime attention should be paid to the official photographic views of stations, instruments, 

 observing party, foreign observatories, etc., for use in illustrations for the published reports. 



6. When necessary to observe dip or intensity out of meridian, make the observations, whenever 

 possible, in magnetic azimuth: o = ± 45°. The same remark appUes to sea observations. 



From Directions of August 5, 1907, to W. J. Peters, Sitka, Alaska. 

 In the future ocean and land magnetic work, the following decisions are to be observed: 



a. The determination of constants for sea dip-circles 169 and 189 should also include 2 sets of 

 regular-dip observations with the suspended needle used in deflections, but not reversing polarity. 



b. The vibration observations with the Kelvin card may be discontinued. [These observations 

 had been extended over a period long enough to show that the vibration method of obtaining inten- 

 sity, with the present appliance, would not be satisfactory.] 



c. In order to facilitate swings, the deflector observations may be reduced to 2 sets, instead of 4, 

 as hitherto, on each heading. On the first-helm swing, one deflector magnet will be used throughout 

 and in the other-helm swing the second magnet will be used. Should experience show that this 

 reduction in the number of sets is not advantageous, you are at liberty to increase the number. 

 Furthermore, if there are cases in which it is more advantageous to make a swing first for declination 

 deviations alone, and thereafter for the other elements, you are authorized to do so. 



d. The sea-deflector observations on course will require special attention. Both lubber-lines 

 will invariably be read. The same method as employed at Sitka will be used. In order to vary the 

 conditions somewhat, make sets as follows : 



(1) "A" of azimuth-circle bows towards observer. 



(2) "B" " " " " 



(3) "A" 



(4) "B" 



Similarly 4 sets with the other magnets. 



e. Whenever there is choice as to sea dip-circle, give preference to 189. 



/. At Honolulu, obtain the intensity constants for the two sea dip-circles for as great a range of 

 temperature as may be possible. For sea deflector 2 (D2), after the observations have been made on 

 8 points for both magnets, then make them on the intermediate 8 points at a temperature differing as 

 widely from the first set as conditions permit. 



From Instructions or May 2, 1908, to W. J. Peters, San Francisco. 



1. Upon arrival at San Francisco, you will carry out all observations in connection with the 

 swings of vessel which may be necessary for the satisfactory and complete reduction of the ship 

 observations. Before making any alterations of vessel, please wire your opinion as to the satis- 

 factory outcome of observations. It will be highly desirable to make complete swings on at least 

 two days for all elements. You will be informed later whether to proceed with alterations. 



2. The principal land-station for the testing of instruments will be Goat Island, as in 1905. 

 Observations at this point should extend over at least 2 days to secure a satisfactory determina- 

 tion of secular change. San Rafael is likewise to be occupied on 2 days. * * * 



