PLOUGH AND PLOUGHING. 



better when it is tjiIkm- drier or moist- 

 er, it is very liillictill to determine, 

 by experiment only, what may, on 

 the whole, be the hesl tiliape. A lit- 

 tle reflection, and the application of 

 scientific principles may greatly as- 

 sist us here. It is not sufficient, 

 however, to find the curve which 

 will make the plough go through the 



ground with the least force. The 

 ploiigli must also perform its work 

 perfectly, and if anything is to be 

 sacrificed, it is better to employ more 

 power than to plough the ground 

 badly. After having ascertained the 

 mechanical principles which bear on 

 the working of the plough, we must 

 observe its action carefully, follow 

 the plough day after day, in different 

 soils and different weather, and thus 

 we may be led to observe all the cir- 

 cumstances which attend its opera- 

 tion, and correct any mistakes which 

 an erroneous theory might have led to. 

 " Many attempts have been made 

 to ascertain the exact curve which 

 the turn-furrow should have to per- 

 form the work well, ^nd at the same 

 time to produce the least resistance. 

 The difficulty of the problem lies in 

 determining tlie data, or principles 

 on which the investigation is found- 

 ed ; and these are so various that it 

 is not surprising that no very satis- 

 /actory conclusion has yet been ob- 

 tained. We will make an attempt at 

 a solution from a simple examination 

 of the motion to be produced in the 

 portion of earth to be turned, which 

 we call the furrow-slice. We shall 

 suppose this separated from the ad- 

 jacent soil by the vertical cut of the 

 coulter, and, at the same time, from 

 the subsoil by the horizontal cut of 

 the share : a section of the slice, by 

 a plane at right angles to the line of 

 the ploughing, will be a parallelo- 

 gram A B D C (Fig. 4), the depth, 



692 



C D b b' 



A C, being the thickness of the slice, 

 and A B its width. Confining our at- 

 tention to this section of the slice, 

 the object is to move it from its po- 

 sition, A B D C, as cut off by the 

 coulter and share, to that of b' d' c' a', 

 where it is inclined at an angle of 

 45° to the horizontal line, the surface, 

 A B (i' a'), being laid on the slice 



