64 



Report on Trials of Flows. 



it ill fuller detail. It will be observed that Mr. Rhaiii's mould 

 board is curved in the form of the spiral thread of a screw, such 

 as would be generated by a line moved 

 uniformly forward in a direction at right 

 angles to its length, while it revolved 

 uniformly round one of its extremities. 

 This surface is thus generated mechanic- 

 ally — Fig. 59. Take a rectangular paral- 

 lelogram, A B C D, of the width of nine 

 inches, or as wide as the intended furrow, 

 and of length equal to four times the 

 width. Bisect B C in E, and D C in F ; at 

 F raise a perpendicular to the plane of 

 the rectangle at F, and make it equal to 

 C E ; join E G, and produce it to K, 

 making K G=E G join K D. Draw from 

 every point in C D lines at right angles to 

 C D, meeting the line E K in ditferent 

 points, these lines will form the required 

 surface. The line K D will be found in- 

 clined 45 degrees to the horizon at the 

 angle K D H, wdiich is the inclination at 

 which the furrow slice is most advantage- 

 ously laid. To those wdio are not familiar 

 wdth solid geometiy, these lines may be 

 "^ easily exhi])ited by means of a wure in- 

 J^/^. 59. sertod at E and bent at a right angle at K, 



inserting the bent portion into the board, A B C D, Fig. GO, at 

 D, lying in the direction E K, Figs. 59 and 60. Care must be 

 taken that G F be equal to C E, and H perpendicular to the 

 board. It is evident that, as the plow moves on, a particle at E 

 will slide along the line E K, become at G perpendicular to the 

 l)lane of the sole, and at K be at an angle of 45 degrees with that 

 A B 



F'f'O. 60. 



