34 TRENCHING AND SUBSOILING 



the periphery, above it the pole socket-head runs loose on 

 the shaft, but may be clamped to the plate by a jumping 

 cotter. A pawl prevents the drum unwinding in the case of 

 the horses backing. It also prevents accidents which might 

 arise from a swingle-bar or pole breaking during the work. 

 If such a breakage occurred, the strain on the cable would 

 cause the drum to revolve backwards, carrying in its rotation 

 the pole, which might injure animals, driver, or onlookers if 

 too close. 



The jerky, clicking noise produced by the falling of the 

 pawl on the ratchet-wheel arouses the attention of the driver, 

 renders the supervision easier, and breaks the monotony of 

 the work. The radius of the drum is 12 inches, and reaches 

 16 inches when the cable is wound up. The pole is 16 

 feet in length ; the moving power is, therefore, multiplied by 

 12*5. The speed of the plough may be increased a little, and 

 the power diminished, by inserting wooden sectors between 

 the flanges of the drum, which increases its diameter. The 

 same result may be obtained by yoking the animals nearer 

 the axis of rotation, that is to say, by diminishing the length 

 of the pole, which is easily done by hooking the swingle-bar 

 to hooks fixed on the pole for this purpose. 



The animals, two or four in number, are yoked to one or 

 two poles, as the case may be. 



The cable is not fixed directly on the plough ; it is fixed 

 on a cable-carrier, which is secured to the plough by chains. 

 This cable-carrier, which is the characteristic of this system, 

 consists of an axle and two large cast-iron wheels (Fig. 14). 



Fig. 14. Cable-carrier used with Bourguignon's Gin. 



