PLATE XVI i. Curves, showing the tlactaotions of index number3 for N, K., H, 0,7, and G with respect to t^ respectively. 



T' r 



Stand witli "o." grade 



-\- 



Stond wilh"b'' qrade 



-4 h- 



10 !0 JO 4« 



I I 



W 



T 



stand with V grade 



>» 



/ / 



Tf 



IN 



to 10 10 Zt 3D 40 50 to ™.ea,M " '" 2" 30 40 50 tn TO 



yeibrs 



Aae 



Age 



"year^ 



