252 



Ocean Magnetic Observations, 1905-16 



The adopted intensity-constants, C,, C^drs, and Cjom, are given in Table 61. For 

 Cruise I they are obtained from a graphical adjustment of all the available data. For 

 Cruises II and III the values in Table 61 are those determined at shore stations for the 

 dates given ; for sea stations a direct time interpolation is made between the next preceding 

 and the next following values of the table. The adopted value of the temperature factor, 

 q, is 0.0001 for both log C, and log Ca. To refer a value at 20° centigrade, taken from 

 Table 61, to the temperature, t, of observations, the following formulae are used: 



log Cu = log Cm -0.0001 (20°- t) 



log C^ = log C,2o +0.0001 (20°- 



Sea dip-circle 203. — Sea dip-ch'cle 203, manufactured by Dover, is of the latest pattern 

 (see p. 195). It was carried as a reserve instrument and was used only at a few auxihary 

 land stations during Cruise I; the corrections adopted for these, from intercomparisons 

 with earth inductor 2 and circle 201, are: mean of needles 9 and 10 at dip +67°, -6(9; at 

 dip +54°, — 4!6; needle 5 at dip +54°, — 5!0. The logarithms of the adopted combined 

 intensity-constant, for needles 7 and 8 (8 loaded with weight 31), in October 1909 are: 



Log C for short deflection-distance, 9.55463 

 Log C for long deflection-distance, 9.48089 



CONSTANTS AND CORRECTIONS FOR LAND INSTRUMENTS. 

 Descriptions op Magnetometers, Dip Circles, and Earth Inductors. 



The reduction formulae and methods of detennining constants for the land instrmnents 

 used in the Carnegie shore work and in the standardization of the ocean instruments during 

 1909-1916 were the same as those in Volume I (pp. 22-41). 



The types of magnetometers used are described and illustrated in Volumes I (pp. 2-7) 

 and II (pp. 5-12) ; the details respecting them, and the adopted constants for the period 

 1909-1916, are shown in Table 62. 



Magnetometers 2, 3, 4, 5, and 8 were manufactured bj' the Bausch and Lomb Optical 

 Company of Rochester, New York; the magnets are hollow cylinders, the long magnets 



