238 



Ocean Magnetic Observations, 1905-16 



Table 57. An examination of the data showed that there were no periodic corrections to 

 log mC, as was the case for the deflectors 1 and 2, used in the Galilee work. In the table, 

 AT=(r-1911.24). 



Table 57. — Intensily Constants of Sea Deflector 4, for Cruise II. 



'Magnet 3 was not used at sea. 



^Deflection distances 1 and 3 only were used at sea. 



The constants adopted on the basis of C. I. W. standard (see p. 232) for sea deflector 

 4 during Cruise III are given by the following equations: 



Magnet 45 log mC = log mC at 20° f or t + . 00026 (20° - 1) 

 Magnet 2L log wC = log mC at 20° for t+O. 00014 (20°-i) 

 Magnet 3 log mC = log mC at 20° f or r + . 00025 (20° - 1) 



The values of log mC at 20° centigrade and for the time r, are taken from Table 58, 

 which was constructed from the time graphs actually used in the final reduction of the 

 observations. The range in the values of Z for this cruise was very small, and there was 

 no indication that the results would be improved by such an adjustment as was made 

 for Cruise II. 



Discussion of changes in intensity constants of sea deflector. — As already stated (see p. 

 236), the intensity constant, mC = H sin u, is subject to change^ because of (1) the effect 

 of change in the temperature, t, both on the magnetic moment, m, and on the deflection 

 distance, r; (2) the effect arising from the aging of the deflecting magnet and the conse- 

 quent time-change in m; and (3) the effect due to cha nge in the vertical intensity, Z. 



'It is assumed that possible changes in the distribution coefficients, P and Q, for the deflecting and compass magnets, 

 and in the induction factor n (n = mh, where h is the induction coefficient for the deflecting magnet), are so small as to be 

 negligible for work at sea. 



