216 



Ocean Magnetic Observations, 1905-16 



Computation of Declination Observations with Sea Deflector D4 



(Form 22) 



DaU: Sat., Aug. 23, 1913, P. M. 

 Vessel: Carnegie 

 Com'd'r: W. J. P. 



Lat: 39° 44' N 

 Obs'rs: C. and H. 

 Sun's Decl'n: +11?45 



Long: 39° 50' W 

 Comp'r: C. C. C. 

 Reviser: W. J. P. 



Horizontal-Intensity Observations, August 23, 1913. 



Specimen observations of horizontal intensity with sea deflector, D4, are given on 

 form 246, page 217. By consulting the "scheme of observations," page 194, the various 

 entries will be readily understood. Sets I and II with magnet 45 at deflection distances 

 1 and 3 are recorded completely. Two shnilar sets. III and IV, were obtained with magnet 

 2L at deflection distances 1 and 3. The numbers attached to the readings for the deflector 

 and the compass show the order in which the various readmgs were made in the respec- 

 tive columns; for numbers 1 to 5 the columns were filled from left to right, whereas, for 

 numbers 6 to 10 the columns were filled from right to left. It will be observed that for 

 each position prescribed in the scheme of observation, 5 settings were made, yielding in all 

 80 readings each for deflector and for compass. The 5 deflector-readings for distance Ul, 

 north end of magnet E, with corresponding compass-readings, were completed before 

 passing to next position, etc. 



When obtaining the means (1), it should be noted that, m accordance with the con- 

 struction of the deflector, the quantity, 90°, is to be subtracted from readings for north 

 end of magnet east, and added to the readmgs for north end of magnet west. The means 

 (2) are the mean values of the 10 compass-readings in each column. The differences (3) 

 result from subtraction of (2) from (1) for north end of magnet east, and (1) from (2) for 

 north end of magnet west. Were the instrumental adjustments perfect, the differences (3) 

 would be directly the deflection angles, u, affected alone by errors of observation. To 

 elmunate outstanding defects of adjustment, the mean of the 4 differences, for each dis- 

 tance, is the final value of m. 



