OR SUBSOILING PLANT. 85 



three wheels, displaced by the block and tackle K, are 

 shown in position. The additional capstan G is anchored 

 to a fixed point by the chain f. 



Machines such as that above described, with complicated 

 mechanism and smaller mechanical yield than simple-effect 

 capstans, require frequent stoppages in course of work in 

 order to rest the animals. In conclusion, the use of 

 balance-ploughs is of no practical benefit when horses are 

 used. 



STATIONARY WINDING DRUMS. 



When the capstan has to be displaced before every 

 furrow, time is wasted, not only in ploughing the wide head- 

 land on which the machine is displaced, but the horses 

 become also very tired through not travelling on a beaten 

 track, having to walk on new ground after every displace- 

 ment. The whole machine has also to be moved while the 

 plough is hauled back. In 1888 the advantage of using a 

 longer cable, a fixed pulley and a stationary capstan was 

 recognised. The capstan may be stationed in the centre of 

 the block if it is large enough (25 to 37^ acres), or in a 

 corner of the block if smaller. With this arrangement a 

 certain amount of mechanical power is lost* but this loss is 

 relatively small, and is compensated by the facility of the 

 execution of the work, and by the diminution of the width 

 of one of the headlands, but we will see that the anchoring 

 of the fixed pulley requires to be done with the greatest 

 care, and, very often, it cannot be anchored at all in loose, 

 soft ground. 



The installation of the complete plant in working order 

 is shown in Plate V. In one of the corners of the block, 

 a a\ b b' (or outside if possible), the capstan A is strongly 

 bedded. The traction cable t fixed to the plough C passes 

 over the fixed pulley P anchored in n n', hauling the plough 

 in the direction of arrow 1 , and is hauled back in position 

 in the direction of arrow 2. With such an arrangement, 



* To give an idea of the mechanical power lost, we quote the following 

 figures : A traction cable 109 yards long, sliding on the ground with a 

 speed of 3'94 inches per second, requires 4 to 5 kilogrammetres per second. 

 A fixed pulley 31 inches in diameter, mounted on an axle 2%3 inches in 

 diameter, over which a cable passes exerting a traction of 3 tons (resistance 

 of a very powerful trenching plough) requires 67 to 68 kilogrammetres per 

 revolution. The addition of a fixed pulley absorbs an average of 8 to 10 

 per cent, of the traction power of the cable. 



