Wheel and Swing Ploucjhs. 



141 



wheels, it is the result of conviction based upon a series of impar- 

 tial, and I think conclusive, experiments. 



I have understood the question to relate to the following^ 

 ploughs, viz. : — 



The swing -plough, hy which I mean a plough the depth of 

 which is regulated by the line of draught and controlling power of 

 the man who holds it ; and 



The wheel-plough, the depth of which is controlled by two 

 wheels, the one about 12 inches diameter, attached to the beam by 

 a sliding shank and socket on the land side of it, — the other about 

 20 inches diameter, attached to the furrow side of the beam. 



The plough is, mechanically speaking, a portion of a screw or 

 curved wedge forced forward horizontally, with which, in the first 

 instance, the surface of the soil is cleft to a certain depth and 

 width, while the wing or mould-board is so constructed as to lift 

 and deposit the separated portion at a given angle. 



The implement which effects these operations with the least 

 power and cost under ordinary circumstances, and which is at the 

 same time most capable of control, I conceive deserves the 

 preference. 



The first consideration is the comparative draught requisite to 

 overcome a given resistance, and to execute a given amount of 

 work. 



In this primary point, I find that writers on the subject have 

 estimated wheel-ploughs to require a greater power of draught. In 

 theory it might seem that the addition of wheels would add to the 

 draught, but, taking into account the uniform gauge and other cir- 

 cumstances which occur in practice, a different conclusion may be 

 come to, as I shall endeavour presently to show. 



As regards the cause of the diminished force required by the 

 wheel, compared with the swing-plough, it appears to me to be 

 principally, if not fully, explained by the more uniform horizontal 

 motion communicated to the share and sole of the former through 

 the regulating medium of the wheels at the fore-part of the beam, 

 which diminish the shocks arising from the continual vibrations of 

 the implement when balanced between the hand of the plough- 

 man and the back and shoulders of the horse. 1 1 is not 

 contended that wheels so situated act the part of lessening the 

 friction between the sole and the soil; but they keep the 

 rubbing part more truly to its depth, and maintain its horizontal 

 action more correctly ; whereas the horses affect a swing-plough at 

 every step by the irregularity of their proper movement, which 

 has to be counteracted by the effort of the man at the opposite 

 end. Thus conflicting forces are momentarily produced, and 

 continual elevations and depressions of the point of the share take 

 place, together with deviations from the flat position of the sole. 



