NORMAL VARIABILITY. 



G3 



through the formidable thicket of difficulties that bars 

 the path of those who pursue the Science of man. 



Mechanical Illustration of the Cause of the Curve of 

 Frequency. The Curve of Frequency, and that of Dis- 

 tribution, are convertible : therefore if the genesis of either 

 of them can be made clear, that of the other becomes 

 also intelligible. I shall now illustrate the origin of the 

 Curve of Frequency, by means of an apparatus shown in 

 Fig. 7, that mimics in a very pretty way the conditions 



FIG. 7. 



FIG .8. 



FIG .9. 





on which Deviation depends. It is a frame glazed in 

 front, leaving a depth of about a quarter of an inch be- 

 hind the glass. Strips are placed in the upper part to act 

 as a funnel. Below the outlet of the funnel stand a 



