FOR PROMOTING AGRICULTURE. 49 



function of the other is to exert force laterally and oblique- 

 ly to carry the sod so that its upper edge shall go beyond 

 the perpendicular, that it may be inverted by its own 

 weight. And he adds that the form of the mould-board 

 must be such as to present in its passage the least possible 

 resistance, and so require the minimum of moving power. 

 His further proposition is that a mould-board of this com- 

 pound-wedge sort can be constructed according to a mathe- 

 matical formula and by a process so exact, that, in the 

 hands of " any common workman its form will not vary 

 the thickness of a hair." He gives in detail a mathemati- 

 cal analysis of the problem and a description of the method 

 of manufacture. He has in mind in this description a 

 wooden mould-board, and says that in practice it works 

 well and that he has several such ploughs in use on his 

 farms. In his communication to the French Academy he 

 said that it would be well, having by the process wrought 

 out a perfect mould-board in wood, to use it as a pattern for 

 producing working mould-boards of cast-iron, and ex- 

 pressed intention to have such made for his own use. 



The difficulty everywhere had been that no two mould- 

 boards were alike ; that the most skillful plough-maker 

 could not duplicate another's work, nor, " except by good 

 luck," repeat his own successes ; and that " when the mak- 

 ers of good ploughs died, their art died with them." The 

 merit of the discovery made by Mr. Jefferson was recog- 

 nized by both the institutions named. An authoritative 

 writer upon the subject says that the credit to be given 

 him must be restricted to his demonstration that ploughs 

 could be made by rule, and to the actual discovery of one of 

 the rules that are applicable to the formation of the mould- 

 board. 



In an official printed list of persons" recognized as " origi- 

 nal members '' of the Massachusetts Society for Promoting 

 Agriculture, appears the name of Timothy Pickering. At 

 the date of the organization, and for many years afterwards^ 

 he resided near Philadelphia, and was also a member of the 



