comstock's rotaey spader. 149 



animals, the driver riding on a seat. Sometimes two ma- 

 chines are attached together, and both are driven by one 

 man. It is used only on land free fiom sod, such as com, 

 or other stubble, and is not adapted to land containing 

 stones or rocks. 



Its advantages are the following : Greater ease of 

 draught, when compared with the plow, the chief source 

 of friction being the thrusting of tlie teeth into the soil, 

 while the friction of the plow at the mould-board is usu- 

 ally equal to at least half the weight of the moving sod, 

 added to half the entire weight of both plow and sod, on 

 the sole in the bottom of the furrow, while more force is 

 required to cut with the edge of the share than with the 

 points of the rotary spader. Hence it is found to do 

 twic/e or three times as much work with the same team as 

 a plow. It does not form a hard crust in the bottom of 

 the furrow, like the plow ; and it leaves friable soils pul- 

 verized ready for planting, without the use of the harrow. 



There are some serious drawbacks to the general intro- 

 duction of this machine. Its cost exceeds ten times that 

 of a good steel plow, while its complexity renders it more 

 liable to strain or breakage, except in uniform and stone- 

 less soils. It cannot be used in wet seasons, and pulver- 

 izes such land only as is previously free from grass. It 

 may, however, prove valuable on extensive farms. 



CLOD-CEUSHEES. 



In clayey soils, clods are often formed in abundance 

 during the process of cultivation. These become very 

 hard in diy weather, and prevent the proper extension of 

 the fine roots of plants in search of nourishment, and also 

 the intermixture of manure with the soil, without which 

 it has been found that two-thirds, or even three-fourths, of 

 the value of manure is lost to growing crops. 



Different modes of pulverizing the clods have been 



