114 



On ylgrlcultural Mechanics. 



The bridle of the plough admits of the attachment of the draught-chain 

 to the plough iDeing shifted to the right or left ; and so it enables the 

 ploughman to increase or dimhiish the width of his furrow ; and the 

 bridle, by means of a screw or otherwise (see annexed figures), may be 

 elevated or depressed, and so the depth of the furrow may be increased 

 or diminished.* 



3. The Mould- Board. 



We now come to the consideration of the third portion of the plough, 

 the mould-board. This, we shall find, is the only portion which requires 

 to be varied; and even in this single point it is questionable how far 

 economy would require a variety of forms. 



In inquiring what is the proper form of the mould-board, the pro- 

 priety of first making an implement to do perfect work, and then 

 altering it to diminish the power required to work it, ought to be 

 attended to here more than it has ever been before ; for Mr. Pusey's 

 experiments have shown how small a portion of the draught is due to 

 the friction of the earth against the mould-board, and how large a por- 

 tion is occasioned by the weight of the plough as it runs along the bottom 

 of the furrow. If, then, v^-e can make a mould-board which answers all our 

 expectations, in the way of the excellence of the work it performs, care 

 should be taken, in altering its form, merely to diminish the force re- 

 quired to work it ; for by so doing we can at best make but a slight 

 variation in that which is but a small portion of the draught. With 

 regard to the position of the mould-board, it should not encroach on the 

 cutting parts of the plough. The furrows-slice should be perfectly cut 

 before any attempt is made to raise and turn it into its ultimate position. 



* There is another and very simple M^ay of altering the depth to which 

 the plough runs ; and this is by changing the position of the back-band. It 

 M'ill be seen that by the action of this part of the harness a portion of the 

 draught is thrown on the back of the horse, and only a portion of it remains 

 on its shoulders. By shifting the back-band nearer to the plough, we increase 

 the ascent of the line of draught, and of course tend to raise the point of the 

 plough, make it work shallower ; and by placing it nearer the shoulders of 

 the animal, the plough is allowed to go deeper. 



