Jan. 28, 1918 Study of Plow Bottoms 1 73 



ie) Shearing, stretching, or compression on each of the remaining five 

 sides of the particle, due to its contact with other soil particles. 



The force which produces the movement of a soil particle in any direc- 

 tion will be the resultant of the components of the above-listed forces 

 which act in the direction of the movement. 



The preceding analysis of the motion which certain soil particles 

 have in the operation of plowing has not been developed from- as refined 

 methods nor as uniform data in all cases as could be desired, but the re- 

 sults obtained furnish abundant evidence that the problem here at- 

 tempted is by no means hopeless. The study should be continued upon 

 a tough sod, which would stretch more uniformly, and some apparatus 

 which would remove the necessity of certain soil particles remaining iu 

 line with each other should be substituted for the pins. 



HISTORY OF THE DEVELOPMENT OF PLOW BOTTOMS 



The Annual Report of the New York State Agricultural Society for 

 1867 contains an ex- 

 cellent treatise giving 

 the geometrical con- 

 struction of the sur- 

 faces of many histori- 

 cal plow bottoms, but 

 no attempt has been 

 made in that report 

 to classify these sur- 

 faces upon the basis 

 of their mathematical 

 forms. Using the above-mentioned work as a basis, the author has 

 attempted to work out the mathematical forms of the most important 

 of these historical surfaces with a view to making fundamental compari- 

 sons with present-day plow bottoms. 



JEFFERSON'S PLOW BOTTOM 



In 1788 Thomas Jefferson, while making a tour in Germany, devel- 

 oped what appears to be one of the first methods recorded for making the 

 surface of the moldboard geometrically exact in form.* He argued that 

 the offices of the moldboard were to receive the soil from the share and 

 invert it with the least possible resistance. In order to do this, Jeffer- 

 son developed a surface which he considered best adapted for the work 

 of plowing, but attention should be called to the fact that no evidence" 

 is offered to prove the assertion. Figure 15 shows the framework for 

 generating the Jefferson moldboard, in which lines em and oh are the 

 directrices. To generate the surface a straightedge is laid upon eo and 



1 GouiD, J. S., et al. Op. cit., p. 403. 



from Report N Y. Stole /Igric.Soc. 1867 



Fig. is. 



