History of the Plow. 59 



the wood that occurs to interrupt it behind the zero, until it 

 applies everywhere behind that line without obstruction. At the 

 third division beyond the zero the pattern may be cut off in a 

 right vertical, though this is not imperative, as the mould-board 

 may be made considerably longer or a little shorter, without at 

 all affecting its operation. At whatever distance in length its 

 terminal edge may be fixed, that portion of the line of transit 

 Avhich lies between the zero and the terminus must leave the 

 original curve, h m d, Fig. 123, at a tangent, and it will reach the 

 terminus as such, or it will gradually fall into a re-entry curve, 

 according as the terminus is fixed, nearer to or farther from the 

 zero line, the terminus of the line of transit being always nine- 

 teen inches distant from the land side plane. That portion of the 

 surface which now remains unfinished between the arcs, a t and 

 d n, Fig. 126, is to be worked off in tangents, applied vertically 

 to the arc, a t, and terminating in that part of the line of transit 

 that lies between d and u. Such portions of the interior cylin- 

 drical surface as may have been formed under the application of 

 the temporary bevel to the arc, a i, are now also to be cut away 

 by a line passing through the junction of the tangents, t a', t b\ t v, 

 Avith the cylindrical arc, a t, forming a curved termination in the 

 lower part, behind, as seen in Fig. 127, which completes the 

 surface as proposed. The breast curve and the form of the 

 npper edge will now have assumed their proper curvature, and 

 there only remains to have the whole pattern reduced to its due 

 thicknesses. This, in the fore i)art, is usually al)out one-half inch, 

 increasing backward below to about one inch, and the whole 

 becoming gradually thinner toward the top edge, where it may 

 be three-sixteenths of an inch. 



We may now sum up the modern history of the plow in Scot- 

 laud by saying that all the plows now in use there are formed on 

 one of the three models which we have described, viz. : Small's, 

 Lanarkshire and Stephens'. The Berwickshire has the lines of 

 the mould-board concave, and the western Fifeshire very sharply 

 convex, but the differences are too unimportant to make a minute 

 description necessary. 



We now proceed to relate the more modern histoiy of the 

 plow in England. We have already stated that the Rotherham 

 plow was the basis of improvement in England, as well as in 

 Scotland, although its progress in the latter kingdom was exceed- 

 inglv slow, for reasons which we have previous] v given. 



