EXTRACTS FROM DIRECTOR'S INSTRUCTIONS FOR CRUISES AND 

 OBSERVATIONAL WORK ON THE GALILEE. 



The following extracts from the Director's instructions and letters to those in 

 command of the vessel will serve to explain the routes followed by the vessel and 

 the methods of observation adopted for the various kinds of work. While some of 

 the early methods, according to experience gained, were modified or superseded, 

 their complete presentation here will be useful in showing how the observations 

 were made at the successive stages of the work, and how the methods and instru- 

 ments were gradually developed and improved. The comparison of instructions 

 for observations aboard a magnetic ship with those for the work on a non-magnetic 

 one (see pp. 316-324), will be of interest, and will show the great superiority of hav- 

 ing a vessel specially adapted for the problem undertaken. The extracts form thus 

 also an historical record of the experiences it was necessary to pass through before 

 reaching the goal set. 



When referring to "swings" of vessel, the term " first helm" is used, regardless 

 whether vessel was swung first with starboard or with port helm. The term 

 "other helm" signifies that the vessel was swung next with helm opposite to that 

 used first. Thus, if for any series of swings, "first helm" is the starboard-helm 

 swing then "other helm" is the port-helm swing. 



CRUISE I OF THE GALILEE. 1905. 



J. F. Pratt in Command. 



From Instructions of Aug. 1.5, 190.5, to J. F. Pratt, San Diego, Cal. 



1. Upon completion of the necessary alterations on the Galilee you will proceed with her to 

 Honolulu, Hawaii, thence work northward as far as the conditions will permit, returning once more 

 to the Hawaiian Islands, if considered best, thence to the Midway Islands, and return to San Fran- 

 cisco^ about December 1, 1905. (This is a general outline of the region to be covered, the precise 

 manner of execution for the successful conduct of the work being left to your judgment.) 



2. The necessary swings for the determination of the deviations in the declination, dip, and 

 intensity will, of course, again be made at the time of departure from San Diego. (For the harbor 

 swings, whenever possible, 16 equidistant headings'* should be taken.) It is especially essential that, 

 during these swings, all articles likely to affect the instruments be in same position as at sea. In this 

 connection you are urged to pay special attention to the iron at the head of the sail when down on the 

 boom, in which position it may come too close to the dip-circle position. In general, the same 

 methods are to be pursued as at San Francisco, except that observations with sea deflectors are to 

 be made as follows: First 8 points use magnet 45, letters on magnet up, next 8 points use magnet 

 45, letters down; for swing on other helm, use magnet NL, letters up, on 8 points, and then on 

 remaining 8 points, letters down.' As much time as possible should be given on each heading, 

 and the list, roll, and any other pertinent data be noted. 



3. If not already done, deflection observations should be made ashore with magnets 45 and NL 

 (letters up and down), so as to determine the constants anew. Likewise the times of oscillation of 

 the two Kelvin cards, as at San Francisco, are to be obtained. 



'Changed later to San Diego. 



'Changed to 8 equidistant headings, experience having proved this number sufficient for the Galilee. 



'Changed subsequently in accordance with footnote 2. 



U5 



