SCIENCE OF THRESHING. 27 



The separating devices in use may be divided into 

 three general classes: first, the kinds wherein the 

 straw is given an intermittent or step by step move- 

 ment through the machine by means of a vibrating or 

 oscillating rack or table; second, kinds where the 

 straw is given a continuous onward movement by 

 traveling raddles; third, where the straw encounters 

 a combination of these two mechanisms. 



There are also accessories such as revolving pickers, 

 racks, beaters and fingers which will be duly consid- 

 ered. 



THE RACK. 



The rack or table usually consists of a series of 

 grates or parallel slats arranged to carry the straw, 

 while allowing the grain to fall through. 



In some forms of racks a series of risers are placed 

 on the surface, which have lifting fingers which are 

 operated by a lever and shaft; they tilt backwords 

 along the rack and are given an up and down motion 

 as the rack vibrates, lifting and tossing the straw as 

 it passes over them, 



