]88 Piogress of Agricultural Knowledge 



li^lit in weight it will be light in draught ; but this supposition 

 is a mistake^ as the report of our judges at Bristol will show. 

 The lightest weight of a wheel-plough there stated is that of the 

 plough which was heaviest but one in draught ; and the swing- 

 plough worst in draught was the lightest in weight of its class. 



Draught. Weight. 



Howard's wheel-plough, lightest in draught .... 22 stones. 220 lbs. 

 Carson's wheel-plough, heaviest hut one in 



draught 32 193 



Earl of Ducie's swing-plough, lightest in draught 26 161 



Wilkie's swing-plough, heaviest in draught 44 125 



This distinction between lightness of weight and of draught 

 should be observed by the makers of ploughs who intend to com- 

 pete at future trials ; and it is satisfactory to the employers of 

 ploughs, since it shows that solid construction of the implement 

 is by no means inconsistent with ease to their horses. Again, if the 

 weight of the plough has little effect on its draught, I believe that 

 the weight of the earth to be raised has not much more — for 

 the furrow-slice, when the plough has severed it, can be turned 

 over by the hand without much exertion; neither can the per- 

 pendicular cutting of the earth by the coulter occasion much 

 of the draught in ordinary land, because implements with nume- 

 rous teeth, each performing a similar cut, can be drawn by four 

 horses. But a plough, when merely drawn along the surface of 

 a furrow, requires considerable force to move it. This arises of 

 course from friction — the resistance of the rough particles of 

 the soil to its progress. If the furrow were coated with ice, a 

 fuiger would draw the plough. Locking the wheel of a waggon 

 at a descent shows the power of this kind of friction. Before 

 the iron shoe is placed under the wheel the horses may scarcely 

 be able to hold back the waggon ; afterwards they may be 

 obliged to pull it : but when the plough is at work, every part of 

 it below ground grates downwards, sidev.ays, or upwards, against 

 the earth, as the shoe of the wheel grinds the road. You must 

 therefore add to the labour of a plough-team when you increase 

 the rubbing surface of the sole or of the mouldboard. Our manu- 

 facturers of implements should, I think, therefore inquire whether 

 they may not improve the draught of their ploughs by diminish- 

 ing the surface of the parts which are below ground. Captain 

 Carr pointed out to me that the draught of a plough is diminished 

 if the coulter be set towards the land-side. The reason must be 

 this, — that the coulter so set prevents that side of the plough from 

 rubbing against the land. 



There is another cause of draught, which, though similar, is not 

 precisely the same with friction. In my first trials I found that a 

 plough drawn along a furrow on clay-land in a very wet state 



