MAGNETIC OBSERVATIONS. 



219 



Hence 



FORWARD RITCHIE COMPASS. 



= + -o5S + 14.000 A, 8.825 l + 4.717 C, 1.631 D l 1.090 E l 

 -. + 0.2058 8.825 A, + 7.545 B, 0.816 C, + 0.934 Z>, + 4.272 ., 

 o = + 0.6749 + 4.717 A, 0.816 A + 6.456 C, 4.554 D, + 3.784 l 



o = _ 0.0407 + A + i (A 2 c*) 



o = + 0.0013 + A + A Ci 



^, = + 0.0477 = + 2 43'-8 

 A = -f- 0.0116 = -|- o 39.9 

 C l = 0.1051= 6 1.3 



A=+ 0.0462 = + 2 38.7 



1 = 0.0004 = o 1.3 



For convenience of reference the values of the coefficients A lt B lt Ci, D lt E u 

 obtained at stations where the compasses were not read on all the thirty-two points, 

 have been collected in the following table. No use has been made of them. 



At a number of the ports visited during the cruise, the line dividing the north 

 from the south polarity, on the exterior of the turrets, was traced out; but as the 

 boundary between the two kinds of magnetism was frequently very badly denned, 

 and the observations were otherwise unsatisfactory; and further, as they throw no 

 light whatever on the theory of the deviations of the compasses, and can only be 

 shown by means of drawings on a rather large scale, it has not been deemed worth 

 while to insert them here. 



In conclusion, the results of the observations made during the cruise may be 

 briefly recapitulated as follows: 



1. The latitudes of seven points have been determined. 



2. The magnetic declination, inclination, and horizontal force, have been deter- 

 mined at eighteen places. 



