INSTALLATION OF TRENCHING 



the width of the headlands / f may be reduced to a 

 minimum. When the pulley P is very far away from the 

 capstan A, it is advisable to use fixed runners x ; these will 

 be studied later on. Plate VI. shows diagrammatically 

 the arrangement for trenching or subsoiling a large block 

 a b c d\ the capstan A is stationed in the centre of the 

 block, which is divided into four sections, e a f A, A / b g, 

 A g e h, e A h d, ploughed in the direction of the arrows 

 using a fixed pulley u. The headlands are also ploughed 

 without moving the capstan, in the direction shown by 

 arrows n, by fixing the pulley in e and g on the lines a c/, 

 b c. With 328 yards of cable, 20 to 22 acres may be 

 ploughed with this arrangement without moving the 

 capstan. 



Sometimes the capstan A 

 (Fig. 52), is placed in the gravi- 

 tation centre of the surface to be 

 ploughed, and, without using any 

 fixed pulley, the plough C works 

 in the direction of the radii, as 

 shown by the dotted lines ; but 

 this arrangement, which does 

 away with the fixed pulley and 

 the waste of power incidental to 

 it, necessitates the ploughing of 

 convergent furrows, which are 

 difficult of execution, and, if the 

 workmen are not closely super- 

 vised, they leave portions of the 

 ground unploughed. We visited 

 a block ploughed by this system ; 

 7 per cent, of it had not been 

 touched by the plough. 



The installation of stationary capstans allows the use of a 

 second cable, as shown in Plate VII. The drum A hauls the 

 plough C, in the direction of arrow I by the cable t passing 

 over the pulley P. The drum B revolving in an opposite 

 direction, hauls the plough back by the cable r passing 

 over the pulley u, in the direction of arrow 2. It is advisable 

 to support the cable r on runners m moving sideways auto- 

 matically with the cable. 



Stationary capstans are built so as to be worked either 

 by horses or steam power ; Pelous' drum (shown in Fig. 53) 

 is an example of this principle. 



Fig. 52. 



