228 POWER AND THE PLOW 



culties. Within the last few years several plowing motors based 

 on the latter principle have been brought to the working stage, 

 using a pulley around which the cable passes only once or twice; 

 the cable otherwise remains stationary, fastened at both ends, 

 or at least at the end of the field toward which the machine 

 is proceeding. As the pulley is made to revolve by the motor, 

 the friction between its surface and the loops in the cable be- 

 comes great enough to propel the outfit. The loss in slippage 

 of the cable on the pulley is claimed to be slight. This system 

 appeals forcibly to those who have seen how ineffectual at 

 times are the efforts of any type of traction wheel and grouters 

 to grip soft ground. One successful motor of this type was 

 ordinarily propelled by traction wheels, but brought the cable 

 into play automatically when the slippage of the wheels ex- 

 ceeded a certain per cent. This rendered the tractor available 

 for use where it was impracticable to use the cable, as on roads. 

 The most successful application of power through cables 

 is, of course, the double-engine and cable method of steam plow- 

 ing. In this system steel cables, 80 to 100 rods long, are 

 attached to the implement, which may be a balance plow, a 

 cultivator, a beet-lifter, or a frame under which harrows, rollers, 

 etc., may be attached. One engine remains idle, paying out 

 the cable, while the other winds it up on a drum mounted on 

 a vertical axis underneath the boiler. The traction wheels 

 of both engines remain stationary while the cable is being 

 wound. In this way the entire brake horsepower becomes avail- 

 able for pulling the plows, there being no loss through slippage 

 or the movement of the tractor's weight across the fields. 

 Slippery surfaces do not affect the tractive efficiency, and in 

 many cases permanent roads along the sides of the fields insure 

 firm footing for the traction wheels at all times. Another 

 advantage lies in the absence of any packing of the soil. The 

 shape of the field has less influence on economy than with the 

 direct traction system, but owing to the length and weight of 



