

Mendenhall & Wood. 



Phil. Mag. Ser. 6. Vol. 30. PI. IT. 



Fig.l. 





II i II 



-160°; 

 H=0 



Fig. 2. 



II 



-f80° 

 H = 21,000 













Fig.3. 



1 1 



-160° 

 + 23° 



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F**mi»i n\\ a 



+23 



o 



180 



H=0 



i \ 



-1 80 



H=22 f 000 



