128 OPERATIONS OP TILLAGE. 



to what precise part of this hne the power is applied. 

 Now, without entering into any mathematical investigation 

 of the principles upon which this line is to be determined, 

 it is to be observed, that in a well-made plough, formed 

 on the principles pointed out, this hne, drawn from the 

 usual point of detachment of the draught on the collars 

 of the working cattle, will intersect the sole of the plough 

 at E, a little behind the setting of the share, and a little 

 to the right of the plane of the left side of the instrument. 



" Now, knowing the height at which the point of draught 

 is to be attached to the shoulders of the working cattle, 

 let us suppose 4 feet, and the distance from the point of 

 the share at which the animals of draught can be conve- 

 niently yoked, let us suppose 12 feet, then laying off 

 D F 12 feet, and F B 4 feet, and drawing B E ; it fol- 

 lows that the point at the end of the beam, is that to which 

 the draught is attached. 



'' But the angle which the line E B forms with the 

 surface, is not, as can be shown, constant, but varies with 

 the depth ploughed, and the tenacity of the soil. That 

 the instrument may suit itself to these variations, as well 

 as that any defects in the form of its parts may be coun- 

 teracted, and that the line of draught may be placed in 

 that portion which is required to pull forward the plough, 

 without there being any tendency in the share to sink into 

 the ground or rise out of it, the bridle is fixed at the end 

 of the beam, so as to elevate or depress the hne of draught, 

 as may be required. Should the plough, for example, 

 tend to go deeper into the earth, the line of draught is to 

 be lowered, by means of the bridle, so that it shall form 

 a greater angle B G F ; the effect of which will be to 

 counteract the tendency which the plough has to go deep- 

 er. The same effect will be produced by shortening the 

 traces by which the horses are attached to the draught, 

 and thus increasing the angle. In like manner, by means 

 of the bridle, the point of draught can be shifted to the 

 right or to the left. If the point of the share tends to 

 point to the left hand, in the firm ground, the line of draught 

 is shifted more to the left ; and if to the right hand, it is 

 shifted more to the right. This adjusting of the plough's 



