Porter — The Physical Basis of Precocity and Dullness. 177 
of the total number of girls is 667. Adding up the col- 
umn, 464 is reached at Grade V; to add the girls in this grade 
would make the sum greater than 50 per cent of 1,334. 
The mean lies, therefore, in Grade V. The difference be- 
tween 667 and 464 is 203, which is 61 per cent of 331. That 
is to say, a line drawn at the mean grade of girls, aged 13, 
would divide them into two groups, the one consisting of the 
High School, Grades VII, VI, and 61 per cent of the girls in 
Grade V, and the other, consisting of 39 per cent of Grade V, 
and Grades IV, III, II, and I. The total number would 
thereby be divided into two classes according to success in 
school life, and success in school life, like success in after 
life, is on the average a fair test of intelligence. 
The actual division of the pupils into these two classes 
cannot be carried out until the number of observations at 
each pound in Grade V is multiplied by 0.61 and 0.39, thus 
making two columns, one of which contains 61 and the other 
39 per cent of the observations in the grade. The former is 
added to the number of observations at each pound in Grades 
VI, VII, VIII, and the High School, and the latter similarly 
added to Grades IV, III, IJ, and I. The mean of the one 
group is the weight of the mean precocious girl and the 
mean of the other, the weight of the mean dull girl. 
The weights calculated by this method for children of 
mean dullness and mean precocity are placed in Tables No. 15 
and No. 1€, in which the mean grade also appears. 
TABLE NO. 15. 
The Weight of the Boy of Mean Precocity and thé Boy of Mean Duliness. 
PRECOCITY. : DULLNESS. 
Age. Grades Pounds. Pounds Grades Age 
S03, iy ue SUE S000 We Oe Eos cet cts 30 ee t8 7 
8 .291, II, Il, IV......-.. G8:60+- GL68 -Raa thesis coos coe seeee 8 
GO: OG Fl, Tig 20g Voi cs ono BR.04.- 06.19 1, 44 TT ois. 9 
10 96 TIVO Vy VL. xx O06 00a. Fil, OST eck eiae: 10 
ae SS TS AV Vy VG sete Cobt 0800 E18, STOLL oss este cscs aes 1] 
da AO EVs, Vig VMs 8. 78.98 79.26 1; TE Ty 68 IV sees 12 
5S 02 V, Vi, Vil. Vi as OE «2006 ks I LULL, 38 Visi ii 13 
14 .88 VI, VI, VII, H.S..- 90.57 85.69 II, III, IV, V,12 VI.......14 
15 .VII VII, H. §.... ....105.97 94.78 Hi, 311, TV, Wy Vins. .65 3s: 15 
16.60 VUE BRE 120.96 105.00 I1,III,IV,V,V1,VIL,.47 VIIL.16 
