SCIENCE OF THRESHING. 57 



meshes with sufficient force to keep them cleared and 

 to itself pass up through the layer of chaff and grain 

 as it passes along; but it should not blow fast enough 

 to lift the light kernels very high. There is a differ- 

 ence between strength of blast and speed of blast. 

 The blast should have strength, but not much speed. 

 A horse might be very strong and able to move a 

 heavy load, but not move it very fast. The horse 

 would then be able to go at a constant and uniform 

 speed whether loaded heavily or lightly. So the 

 blast in the shoe should be able to move at its regular, 

 constant speed, regardless of the amount of grain to 

 be handled. It is plain that it should be the strongest 

 at the front end of the chaffer where the load is 

 heaviest, the chaff being mixed with the grain and 

 packed together at that point. After the blast has 

 once penetrated the layer and has lifted the chaff up 

 in the air it does not need as strong a blast to keep it 

 there. In some wrongly constructed chaffers, the 

 reverse conditions are found; the blast being 

 strongest at the rear end of the chaffer and weakest 

 at the front end. In such cases, the heavier the load 

 of chaff which comes in at the front end, the harder 

 the blast will be at the rear, for as soon as a little too 

 much grain and chaff enter the front end and clog the 

 meshes, the blast ceases to escape there and is forced 

 along under the sieve to its rear end; here it is 

 confined and deflected upward by the bottom of the 

 shoe, escaping through the rear meshes with force 

 enough to carry kernels and all along with it. 



If a shoe is found in this condition, the remedy is 



