PLATE XXI. Carves, shawing the iluetuatiin of l', eacfc .stond, compared with tht »/;,»je voliime. 



^'* Curves, showing the flttcluaTion gf t^ -fir each stanJ. ''^^ 



Stonil witK ''a" grade 



Stand with ''b" grade 



Stand with "c" grade 



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^ 



r 



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4 



^ 



i 



la io 30 iO .so ua " 14 U 3« M »» M >0 20 M 4« »^ ••xIAS 



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