Fi^. 15. 



Fv^-26 



ovlcaU 



B ; 





A 



If--: 



■beginruncf 



\ 



tuiulcu" oLpertuj~e- \ 



N 





-■\^v-^-J»- 



■■^^i 





■ vcxZve. 





aperlure. 



...vaZve. 



z^oex:uicy 



Fi^. 18. 



S F Harmpr del. 



