9 6 BIOMETRY 



one of these elements depends upon factors which we 

 have no means of classifying exactly. 



It now becomes necessary to mention one or two 

 technical terms which are used in connection with the 

 normal curve. The mode of such a curve is the 

 longest perpendicular which can be drawn from the 



Q M Q 

 FIG. 8. NORMAL CURVE. 



base-line to meet the curve itself (M in the above 

 figure). The curve is symmetrical on either side of the 

 mode that is to say, any two perpendiculars drawn 

 from the base to the curve on either side of the mode 

 and at the same distance from it will be equal in 

 length. 



When dealing with a symmetrical curve the position 

 of the mode is identical with that of the median the 

 perpendicular line which divides the area of the 

 curve into two equal halves, and the foot of this 

 perpendicular also represents the mean or average of 



