120 Ocean Magnetic Observations, 1905-16 



E The observations should be reduced and analyzed, as soon as possible, and the values of 

 B arid C to the nearest minute and giving sign (whether plus or minus) for the 3 positions wired 

 the Office. The detailed results will be mailed promptly. , ■„ u 



F Throughout above work no other magnetic instruments than those designated will be 

 allowed on the bridge. (You were instructed by wire that the Kelvin compass is to be re- 

 mounted; this applies only to the binnacle, it being not the intention to have the compass bowl 

 mounted on the binnacle, except for occasional experiments at sea, as per directions sup- 



^ G The Galilee will be steadied, of course, for a sufficiently long period on each heading to 

 secure good results. All pertinent facts with regard to the swing and conditions under which 

 made, list, roll, etc., will be fully recorded. 



Directions of January 31, 1906, for Swings No. 2 at San Diego, to W. J. Peters. 



1. Same preparations as called for in paragraph 1 of Directions for Swings No. 1 are to be made. 



2. The special purpose of the second swings will be to determine the inclination and intensity 

 deviations. Besides recorder, 3 persons will be requisite, one at Ritchie standard compass (RIB) 

 to hold vessel on course, to call out to the observers when vessel is on course, and to record for one 

 of the observers. One observer will make horizontal-intensity observations with sea deflector 1, and 

 another will make inclination and intensity observations with sea dip-circle 35. The same remark, 

 2 G, Directions No. 1 , applies here. The swing will be made on 8 equidistant points, with both helms. 



'3 Inclination and intensity observations with sea dip-circle 35.— First-helm swing; both loaded- 

 dip observations (needle 4, weight 6), and regular-dip observations (needle 2), on each heading 

 (scheme A). Other helm: deflection observations (scheme B). Schemes A and B are purposely 

 made elaborate in order to ascertain cause of certain discrepancies which have revealed themselves 

 in past swings. It will be far better to take all positions of circle and of needle on each heading every 

 time rather than to multiply readings for any one position. However, as many readings as possible 

 of both ends of needle should be made for each position. Care must be taken, before mounting the 

 needle that all dust has been removed from the dip circle, especially along the inner periphery of the 

 vertical circle, near which the ends of the needle come, so that when lifting the needle its ends will 

 not gather up fine dust-filaments. Likewise the blade of needle must be thoroughly clean and dry, 

 so as not to introduce an additional balance error. As schemes A and B require rather frequent hand- 

 ling of needle, great care against injury to the pivots must be exercised, and the fingers be dry. 

 The jewels must, of course, also be kept free of dust and moisture. 



Scheme A. — First Helm: Loaded Dip and Regtdar Dip. 



No. of 

 opera- 

 tion 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 



14 



16 



16 



Ship's 

 head 



N 



N 



NE 



NE 



E 



E 



SE 



SE 



S 



S 



sw 



SW 



w 

 w 



NW 

 NW 



Reading of mag. meridian 

 on hor. cir. 



Cir. E. 



Cir. W. 



Operation 



Loaded dip 



Regular dip, A' down. 



Do 



Loaded dip 



Do 



Regular dip, A down . . 



Do 



Loaded dip 



Do 



Regular dip, A down . . 



Do 



Loaded dip 



Do 



Regular dip, A down . . 



Do 



Loaded dip 



' Polarity of needle 2 to be same throughout swing; however, needle should be well magnetized before swing, and so 

 that the A end will be down. 



