148 



MECHANICS. 



more costly implement {Fig. 126). It consists of 

 about two dozen circular cast-iron disks, placed loosely 

 upon an axle, so as to revolve separately. Their outer 

 circumference is formed into teeth, w^liioh crush and 

 grind up the clods as they roll over the surface of the 

 field. Every alternate disk has a larger hole for the 

 axle, which causes it to rise and fall while turning 

 over, and thus prevent the disks from clogging. It 

 can be used only when the ground is dry. 



SECTION III. 

 SOWING-MACHINES. 



Sowing-machines, for wheat and other grains, pos- 

 sess great advantages over hand-sowing. All the seed 

 being deposited by them at nearly a uniform depth, 

 and completely covered with earth, it vegetates and 

 grows evenly, and the plants are uniformly strong and 

 vigorous. A less quantity of seed is required, and the 

 crop is heavier. 



Small seeds, such as carrots and turnips, can be 

 sown evenly and rapidly only by means of drills adapt- 

 ed to these seeds, and hence drilling-machines are in- 

 dispensable in the cultivation of such root-crops. 



A great number of different drills have been made 

 for sowing grain, the general principles of which can 

 be only noticed in this treatise. The seed is delivered 

 by means of a revolving cylinder, in the surface of 

 which small regular cavities have been made, which 

 constantly carry off and drop measured portions of the 

 grain. The motion of this cylinder is increased or less- 

 ened by means of wheel- work, according to the quan- 



