200 



GENERAL BIOLOGY 



general average. If one were to fire a thousand 

 rifle shots at a target and then sort out the results and 

 classify them with regard to the accuracy of the hits, 

 it would be found that the most accurate and the 

 least accurate ones are fewest in numbers, and that 

 the greatest number of hits is somewhere in between. 

 If we plot out the result on paper, in the same way 



FIG. 71. Bird's-eye view of forty men arranged in files by classes of 

 stature. (Davenport.) 



that we arranged the men above described, a similar 

 curve will be secured. The same result will be 

 obtained from any large array of data, the distribu- 

 tion of which depends upon chance. An ingenious 

 device invented by Galton illustrates this mechan- 

 ically. 



A shallow oblong box (fig. 72) is constructed, one 



