104 SPECIAL SUBSOILERS. 



The point of a tine a n describes in the soil a trajectory 

 a a" b disturbing a volume of soil represented in section 

 by f. Practically the section worked is a little larger on 

 account of the tearing taking place in the part a" b. 



We see in diagram 67 that the profile a n of a tine must 

 be inside the cycloid a a! generated by the point a. If this 

 condition is not fulfilled, the back of the tine compresses the 

 soil in the part a a" . This waste of power has also the disad- 

 vantage of forcing the wheel to slide on the ground. 



To obtain satisfactory subsoiling it would be sufficient, 

 after the tine n a has disturbed the part f, for the next 

 tine ri d' to disturb the part d e a, for the zone r is torn 

 away. 



From the above it results that the distance apart n n' of 

 the teeth on the circumference of the disc a, must be at the 

 maximum equal to b a or a cL By setting the tines closer 

 together the section r, which has to be disturbed by tearing, 

 is diminished. 



In Guibal's subsoiler the radius of the disc A was 

 15-7 inches, the length / of tne teeth was 12 inches, the 

 distance apart a of of the points was 11 inches, tha^t is to say, 

 the distance a d' was ^ of the length I of the teeth. If we 

 draw the diagram relative to the work of Guibal's machine, 

 we see that the teeth successively describe curtate cycloids, 

 having within the zone of work the following dimensions : 



Chord a b ... ... ... 15 inches. 



Arrow y a" ... ... .. 12 inches. 



Distance apart of two successive trajec- 

 tories at ... ... ... 6 inches. 



Under these conditions the whole depth y a!' of soil could 

 be thoroughly disturbed. 



When the weight P of the disc is not sufficient to overcome 

 the resistance to penetration of the subsoil, a portion only of 

 the teeth penetrates, the periphery of the disc A not being in 

 contact with the soil. Under these unfavorable conditions 

 the surface of the soil (Fig. 67) must be considered as being 

 x #', and the zone of action of each tine diminishing in 

 depth as well as in width, may leave, in certain cases, por- 

 tions of the soil, untouched. 



It appears that machines built on this principle were dis- 

 carded after 1860. It would be interesting to ascertain if 

 their principle was wrong, or if the construction was defec- 

 tive at that period. Unfortunately we have been unable to 

 find any literature answering this question. 



