Phil. Mag. Ser. 6, Vol. 27, PI. X. 



Fw. 11. 







































/ 

























\ 



































































D 4 



DO 6C 



8 



]Q 10 



00 12 



00 14 



00 \i 



00 \c 



00 



Fig. 12, 



40 



30 























<* 



4 





/ 





















#,*» 







10 20 30 40 50 



