i82 Journal of Agricultural Research voi.xii, no. 4 



following quotation gives a very good description of the Holbrook sur- 

 faces : 



We 1 were interested in the most minute details of these plows by Gov. Holbrook 

 and the trials at Utica and subsequently at Brattleboro, Vt., showed very clearly the 

 influence of the warped surface which is generated by his method upon the texture 

 of the soil. Gov. Holbrook is as yet unprotected by a patent on his method, and we 

 are therefore most reluctantly compelled to withhold a description of it but we have 

 no hesitation in saying that it is the best system for generating the true cvirve of the 

 moldboard which has been brought to our knowledge. This method is applicable to 

 the most diversified forms of plows, to long or short, to broad or narrow, to high or 

 low, no matter what the form may be, this method will impress a family likeness 

 upon them all. There will be straight lines in each running from the front to the 

 rear and from the sole to the upper parts of the share and moldboard. None of these 

 lines will be parallel to each other, nor will any of them be radii from a common cen- 

 ter. The angle formed by any two of them will be tmlike the angle formed by any 

 other two; a change in the angle formed by any transverse lines will produce 

 a corresponding change in the vertical lines, and there will always, in every 

 form of this plow, be a reciprocal relation between the transverse and vertical ^ lines. 

 Plows made upon this plan may appear to the eye to be as widely different as it is 

 possible to make them, and yet, on the application of the straightedge and protractor, 

 it will be found that they agree precisely in their fundamental character. The 

 siuface of the moldboard is always such that the different parts of the furrow slice will 

 move over it with unequal velocities. 



From the above description it is evident that the surfaces of the Hol- 

 brook plows are portions of a hyperboloid of one sheet whose general 

 equation is 



-2+52 ^-i 



MISCElvIyANEOUS PLOW BOTTOMS 



In addition to the surfaces already described there remain at least 

 three which show unique characteristics, but data were not available for 

 developing the equations. 



In 1 81 8 Gideon Davis,^ of Maryland, patented the surface of a plow 

 bottom which was obtained by using the segment of a circle as a gen- 

 erator and two segments of another circle as directrices. Somewhat later, 

 1834, James Jacobs,* another American, brought out a plow bottom the 

 surface of which was a combination of two mathematical surfaces, each 

 of which had sets of straight lines in two directions. 



In 1839 Samuel Witherow, of Gettysburg, Pa., and David Pierce, of 

 Philadelphia, Pa., brought out a plow bottom whose surface was gen- 

 erated by the most ingenious use of the arc of a cycloid. A more detailed 

 description of this plow can be found in the Report of the New York 

 State Agricultural Society for 1867,^ 



* GoTJXD, J. S., et al. Op. dt., p. 586. 



* It should be noted that the hnes here called transverse are designated as longitudinal (PI. 2, A), and the 

 ]ines called vertical are designated as transverse. 



^GoxJiD, J. S., etal. Op. dt., p. 452. 



* Idem, p. 486. 

 *Idem, p. 491. 



