116 Ocean Magnetic Observations, 1905-16 



4. All observations made at San Diego, inclusive of the ship swings, are to be transmitted to 

 Washington, so that the Office can make final reduction of the work done on the trip from San 

 Francisco to San Diego. Abstracts of the essential quantities should be made in the "Abstract 

 Books" left in your possession. 



5. In general at sea, swings on as many points as possible are to be secured, on the average every 

 second or third day, conditions permitting, and observations be made on the intermediate days on 

 the ship's course, again using every precaution as to the position of articles likely to affect the instru- 

 ments. In the sea-deflector work it is preferable to use each time both magnets as per general 

 scheme above, not having, however, on the bridge more than one magnet at a time. 



6. On the course observations. — Dip and intensity observations with sea dip-circle 169 (needles 

 1, 2, 3, 4), and observations with sea deflector 1 should be made according to method followed on 

 experimental trip from San Francisco. It will be well to interchange observers. Thus first day: 

 Dr. Egbert, sea deflector; Mr. Ault, sea dip-circle. Next day: Dr. Egbert, dip circle; Mr. Ault, 

 deflector, etc. The endeavor should be to have the mean time of the deflector work about the same 

 as that for the dip circle. 



7. Should it not be possible to make deflections with the dip circle in low latitudes, then con- 

 tinue, nevertheless, the observation with the loaded needle, and thus secure relative total intensity. 

 The observers must be cautioned to take every possible care in handhng the needles. Should any- 

 thing happen to needle No. 3, preventing its further use, then cable as soon as possible and substi- 

 tute for it one of the dip needles (No. 1 or 2), noting that thereafter the particular dip needle selected 

 can no longer be used for inclination observations, and must not have its magnetism disturbed; it 

 should be kept in the box with No. 4. In case anything happens to the loaded needle (No. 4) so aa 

 to make impossible observations with it, then continue simply the deflections and inform the Office 

 promptly of the accident. It is sincerely hoped, however, that these contingencies will not occur. 



8. Owing to the difficulty in securing declinations, on account of meteorological conditions, it 

 will be necessary to avail yourself of every opportunity to secure data, keeping a man on the lookout 

 on the bridge whenever necessary. The observations should be made over as long an interval as 

 possible, and it will suffice to get them, in general, with the Ritchie standard compass (RIA); 

 however, it will not be amiss to secure comparative data with the other compasses, this being one of 

 the purposes of the expedition. 



9. The Ust, roll, and all other pertinent data must be entered in the record for all observations 

 made. 



10. The general investigation of local disturbances in the vicinity of land-masses must be left 

 to your judgment, this matter being dependent on conditions encountered. 



11. The various instrumental constants and ship deviation-coefficients will again be determined 

 at Honolulu, Hawaii, making use of the facihties at the Coast and Geodetic Survey Magnetic Ob- 

 servatory, so as to check up once more on the instruments. They will also be determined again at 

 San Francisco.' 



12. All navigational data and geographic positions assigned to the observations at sea must be 

 checked by some independent observer, besides the one to whom you will give chief charge of thia 

 work. * * * 



From Directions or September 18, 1905, to J. F. Pratt, Honolulu. 



1. Judging from experience in the discussion of observations made on Coast and Geodetic Survey 

 vessels, and that now being encountered on the Galilee, it would appear that our principal trouble on 

 the latter vessel will arise from the shifting positions of masses of iron, as for example, hoisting-chains 

 and blocks. There are several instances in our observations from San Francisco to San Diego where 

 differences have occurred, which can only be explained by the circumstance that masses of iron may 

 have come too close to the instruments. 



2. You are therefore requested to make a study of the remaining masses of iron in the rigging, 

 sails, and hoisting tackle, which could be replaced by non-magnetic metal, and to make an estimate 

 of the probable cost, so that it may be decided whether the changes can be made when the Galilee 

 returns to San Francisco (San Diego). A critical analysis of the observations thus far shows very 

 clearly that if we can properly control the positions of the remaining masses of iron, a most gratifying 



'Changed later to San Diego. 



