SPECIAL SUBSOILEKS. 



103 



found advisable to use five, the depth of cultivation reaching 

 18 inches. If we consider the above figures we are in a 

 position to see that if we represent by ten the resistance of 

 the unity section of the arable soil opposed to the plough, that 

 the resistance opposed by the subsoil to the digger is eleven. 



In the short days of November, doing only six hours of 

 actual work, the area worked per day was from 136 to 144 

 poles. The whole plant required is the ordinary plough and 

 team, plus five horses, a driver and two men for the digger. 



Let us study the work of one tine of Guibal's machine. 

 If the disc A (Fig. 67), has a weight P, sufficient to- pre- 



Fig. 67. Diagram showing the work of a Subsoiler. 



vent it from sliding, any point of the circumference m 

 describes in the vertical plane a series of curves c'm c c" 

 called cycloids. If the point a is outside the circle, the 

 trajectory described by that point is a curtate cycloid.* 



* We may mention that cycloids (common cycloid, curtate cycloid, and 

 prolate cycloid) are curves generated by a point in the plane of a circle, 

 when the circle is rolled along a straight line, keeping always in the same 

 plane, and possess the following properties : In any point of the curve, 

 the normal to that curve passes by the point of contact of the circle A with 

 the fixed line x. For instance, for the portion a a" b, which interests us, the 

 normals in a and b coincide with the plane x of the soil. In a" the normal 

 y is perpendicular to x x. 



