VARIATION AND HEREDITY 



201 



side of which is of glass. Toward one end a number 

 of longitudinal compartments are formed of strips of 

 tin ; at the other end, a sort of 

 funnel is constructed in the same 

 way. Between the two is a field of 

 pins inserted alternately. The ap- 

 paratus is provided with a handful 

 of shot before the glass cover is 

 put on. When the box is inverted, 

 the shot all run back into the com- 

 partment behind the funnel. 





"Then, when the box is tilted, 

 the shot passes through the funnel, 

 and issuing from its narrow end, 

 scampers deviously down through 

 the pins in a curious and interest- 

 ing way, each of them darting a 

 step to the right or left as the case 

 may be, every time it strikes a 

 pin. The pins are disposed in a 

 quincunx fashion, so that every 

 descending shot strikes against a 

 pin in each successive row. The 

 cascade issuing from the funnel 

 broadens as it descends, and at 

 length every shot finds itself caught in a compartment 

 immediately after freeing itself from the last row of pins." 



When we examine the disposition of the shot in the 

 compartments, we find that the greatest number 

 is to be found in the middle compartment (if the 

 apparatus be held vertically), and that the com- 

 partments on either side contain a diminishing 



FIG. 72. Gallon's 

 mechanical device for 

 illustrating the law 

 of the frequency of 

 error, and the dis- 

 tribution of variatea 

 in the normal curve. 



