322 Ocean Magnetic Observations, 1905-16 



1. Magnetometer 4 (or No. 2, if found preferable) at A, sea deflector 4 at B, simultaneous D 

 and H observations (not less than 3 good sets of each element and with each instrument). For each 

 set, the footscrews, or the bowl as the case may be, will be oriented differently. To overcome 

 possible sticking of the deflector card, drum on glass cover before each reading in both H and D work. 

 The deflector D-observations will be made before and after the deflections by observing magnetic 

 bearing of mark and using lowest part of wire. 



2. Magnetometer 4 at B, deflector 4 at .A ; same observations as for 1. Observers will exchange 

 instruments but not stations. With proper care, the station difference, A-B, will be derived from 

 observations 1 and 2, with sufficient accuracy for the immediate purpose. 



3. Earth inductor 2 at A and D. C. 189, or its substitute, at B; simultaneous observations; 

 dip needles the same as those used in the ocean work, supplemented by another needle for possible 

 future use, as selected by the Commander. Besides regular dips, complete total-intensity observa- 

 tions, inclusive of loaded dip, are required. As many sets as possible (not less than 3 for direct dip 

 and 3 for total intensity) are to be secured. The manner of scraping or tapping the brass knob in 

 observing with sea dip-circle appears to require attention; theoretically, the conditions at sea should 

 be simulated as closely as possible. 



4. Earth inductor at B and D. C. 189 at A, observers exchanging instruments but not stations. 

 Same observations as for 3. (The absolute value of H will be derived from the magnetometer 

 observations of the previous two days.) 



5. Detenminations of declination-constants by Sun observations and bright-line method with 

 deflector 4 during the most suitable time. As many sets as possible under varying conditions are to 

 be secured, not less than two observers taking part. The constants for the marine collimating- 

 compass will be determined as the Conamander may direct. 



6. Such observations as foimd necessary are to be repeated during the available time. 



7. The above scheme requires two careful observers for successful execution. Where compari- 

 sons are to be made with local instrimients, e. g., at Batavia, then these are to be included in the 

 above scheme as found best, a third observer, if necessary, taking part and following the special 

 directions for comparison work. The most experienced observer available is required for the 

 observatory comparisons; on these, special care must be bestowed. 



Instructions of August 13, 1913, for Work at Falmouth. 



Shore Work. 



1. Trefusis Point, as in 1909, to be the main station for general intercomparisons of instruments 

 and determination of instrmnental constants, provided that this station is still found satisfactory; 

 otherwise some suitable place near by is to be selected. The directions regarding reoccupations of 

 old stations will be expUcitly followed. 



2. St. Anthony (C. I. W. 1909) to be reoccupied, using one of the magnetometers and a good 

 land dip-circle, and obtaining complete observations on 2 days. 



3. Porthallow (British Magnetic Survey, 1890) to be reoccupied, as nearly as conditions permit, 

 using a magnetometer and a good land dip-circle, and securing complete observations on 2 days. 



4. Truro (British Magnetic Survey, 1890). Same remark as for No. 3. 



5. Falmouth Observatory. — The complete reoccupation of the observatory station on one day 

 would be desirable. 



6. General note. — All stations are to be marked in some manner, besides taking the usual 

 angles and making such measm-ements to nearby objects as may be possible. 



Ocean Work. 



1. Observations are to be made of the three magnetic elements diu-ing complete swings of 

 the vessel, both helms, arranged in best manner possible, and at such a time as the Commander 

 may find most suitable, the place of swing to be the same as in 1909 (latitude 50° 06' N, longitude 

 5°01'W). * * * 



