s iv.] SCHEMES OF DISTRIBUTION AND OF FREQUENCY. 39 



the height of the vertical lines to be erected at the 

 corresponding Grades when we are engaged in con- 

 structing the Figure. 



Let us begin with the third line in the Table for 

 illustration : it tells us that 37 per cent, of the group 

 had Strengths less than 70 Ibs. Therefore, when drawing 

 the figure, a perpendicular must be raised at the 37th 

 grade to a height corresponding to that of 70 Ibs. on 

 the side scale. The fourth line in the Table tells us 

 that 70 per cent, of the group had Strengths less than 

 80 Ibs. ; therefore a perpendicular must be raised at the 

 70th Grade to a height corresponding to 80 Ibs. We 

 proceed in the same way with respect to the remaining 

 figures, then we join the tops of these perpendiculars 

 by straight lines. 



As these observations of Strength have been sorted 

 into only 7 groups, the trace formed by the lines that 

 connect the tops of the few perpendiculars differs sensibly 

 from a flowing curve, but when working with double 

 minuteness, as mentioned above, the connecting lines 

 differ little to the eye from the dotted curve. The 

 dotted curve may then be accepted as that which would 

 result if a separate perpendicular had been drawn for 

 every observation, and if permission had been given 

 to slightly smooth their irregularities. I call the figure 

 that is bounded by such a curve as this, a Scheme of 

 Distribution ; the perpendiculars that formed the scaf- 

 folding by which it was constructed having been first 

 rubbed out. (See Fig 4, next page.) 



A Scheme enables us in a moment to find the Grade 



