132 MECKANICS. 



width of the furrow is only one-half the depth. But with 

 a single plow, the width must be considerably greater than 

 the depth, or the ^. , 



^ ' Fi;?. 138. 



sod will be thrown 

 on its side or edge 



and cannot be in- 

 verted. There is 



one disadvantao^e, 



, .1 BmUe Michigan Flow. 



however, m the 



use of the double plow. A greater force is required 

 to make two cuts in the soil, one above the other, than 

 one cut with a single share.* For this reason more 

 force must be used to plow a field to a given depth, say 

 one foot, with the double than with the single plow. But 

 the single plow, in order to reach this depth, would re- 

 quire to be so large and to turh so wide a furrow that no 

 ordinary amount of team could be had to do the work. 

 And in addition to this difficulty the inverted surface would 

 not be so well pulverized as by the use of the double 

 plow. 



THE SIDE-IIILL PLOW. 



Side-hill or Swivel plows are well known, and are so 

 constructed as to throw the furrow-slice down hill, which- 

 ever way the team may be passing. The mould-board is 

 turned to the right and left alternately for this purpose, 

 the right-hand horse walking in the furrow in one direc- 

 tion, and the left-hand horse in the other. This plow is 

 sometimes used for level land when it becomes desirable 

 to avoid dead furrows and ridges, "without plowing around 

 the field. Fig. 139 represents the s^tivel plow manufac- 



* This result has been proved by the use of the dynamometer; which 

 has also shown that a greater amount of earth, in cubic feet, may be 

 turned over with a deep-running plow than with a sliallow one, as there 

 is less force expended in cutting the slice wlien compared with the whole 

 bulk x^rovidcd the soil is nearly uniform in hardness at different depths. 



