112 On Agricultural Mechanics. 



those of the Scotch ploughs of Clarke and Fergusson, plough-makers 

 of Stirlingshire (see woodcut). The length of the beam is in these 

 ploughs 3 feet, and that of the handles is 5 J feet; that of the whole 

 plough is lOrr feet, which leaves 21 inches for that part of the frame- 

 work to which the body of the plough is attached. 



The following is a sketch of the mere frame-work of their 

 plough^ on a scale of iVth : — 



[Frame-work of Clark's Plough. Scale -jL.] 



2. The Cutting Parts. 



The cutting parts of the plough are, the share, which cuts 

 horizontally the bottom of the slice, and the coulter, which cuts 

 it vertically from the fast land, of which it forms part. It is 

 evident that these should cut it perfectly. 



There should be no tearing when the mould-board begins to work. 

 Any tearing must require an otherwise unnecessary exertion of power, 

 and will increase the draught. In some districts an invention has been 

 tried which does away altogether with the attachment of the coulter to 

 the beam of the plough, and provides in its place a projecting edge, 

 standing up from the sock on the vertical plane of the side of the plough, 

 but inclining backwards towards the plough, at a considerable angle. 

 This, of course, ensured the perfect cutting of the sod ; but it was found 

 in practice that it encountered more obstruction, and was more liable to 

 bend, or, if made of cast-metal, to break, than the common arrangement 

 for the purpose: it was, therefore, abandoned. It is evident also that 

 the sides of the furrow-slice should be square ; that the section of the 

 sod should be rectangular. It is obvious that as the furrow-slice, sup- 

 posing in the annexed figures a ft c <:/ to be a section of it, must 

 turn around the point d, if the angle ft c r/ is an acute angle, it will be 

 held fast, and must either be thrust aside beyond the reach of the pro- 

 jecting ledge e b c, or forced through it ; either of these takes place 

 under a waste of power. In order, then, to be capable of turning, it 

 must be either rectangular, or the angle bad must be obtuse. Now 

 there are two advantages connected with its being a right angle. A" 

 greater amount of surface will be exposed : compare the two annexed 

 figures (1 and 3). It is evident that, other things being equal, the 

 smaller the angle the greater will be the surface exposed. A greater 

 depth of mould will also be torn down by the harrows, a greater quan- 

 tity of earth being raised above the general level in the form of ribs, 



