History of the Plow. 125 



side, and I then transfer on the surface of the block the gradua- 

 tions on the edge of the gauge, numbered from 4 to 12. 



" I then make a third gauge, Fig. 9, in like manner as the other 

 two, to correspond in every respect witli the arc o, Fig. 6, as the 

 other gauges were made to correspond with the arcs h and A-. I 

 cut and mark the surface of the block on the plane of the first 

 division in the same manner as it was cut and marked by the 

 other gauges in the plane of the second and third divisions, and 

 bearing the same relation to the face of the block which repre- 

 sents the land side that the arc o, on Fig. 6, bears to the line A a 

 or plane of the land side. Having thus cut away the surface of 

 the block to the required concavity in the jDlane of the first, 

 second and third divisions, and marked and numbered thereon the 

 several graduations to correspond with the graduations on the 

 arcs 0, h and h^ of Fig. 6, I then cut away the surface of the 

 block in the direction of straight lines, so that a straight edge 

 Avill touch along the entire length of the surface, passing through 

 the graduations correspondingly numbered on the concavity at 

 the three divisions, as shown on Figs. 4 and 5 by the lines g f^ 

 Ff^ to Ff^^y inclusive, and then work off the remaining portions 

 of the surface between and beyond these lines to a form which 

 will correspond therewith." 



Plows had previously been made approaching in some degree 

 to a cylindrical form, but Mr. Joshua Gibbs, on the 15th of 

 August, 1854, patented a plow which strictly conformed to this 

 principle, as will be seen by the following extracts from his 

 specification: 



" Fig. 72 is an elevation of my improved plow, showing the 

 working side of the mould-board. Fig. — is the representation 

 of the interior of a cylinder from which the mould-board was 

 made. Fig. — is a section of said cylinder. Fig. — , the mould- 

 board as seen when looking at the forward end. Fig. — , the 

 land side and parts connected with it. * * * * 



" The working surface of the mould-board, A, consists of about 

 one-quarter of the interior surface of a hollow cylinder, one end 

 of which is represented in Fig. — , and a section of the interior 

 in Fig. — . If the plow is intended to turn a furrow six inches 

 wide, a mould-board made from a cylinder of about twelve inches 

 bore is desirable; but if it is to turn a furrow twelve inches 

 wide, the mould-board should be made from a cylinder with a 

 bore of about two feet. As these plows have been found to work 



