TRENCHING AND SUBSOILING. 157 



of the brake, then the ploughman places a forecarriage in 

 front of the plough, made of two wheels and an axle bent at 

 a right-angle, and, by a kind of tilting movement, as the 

 plough progresses it is lifted out of the furrow (Figs. 20 

 and 21, pages 40 and 41). Finally, when the plough is com- 

 pletely out of the furrow the drum is thrown out of gear and 

 the motor stopped ; the ploughman takes it back with a horse, 

 while the men at the motor shift it sideways a distance equal 

 to the width of the furrow. This is done with an ordinary 

 crowbar if the land is level, and with a screw-jack if it is 

 rising; twelve furrows are opened in this manner, when 

 another pair of rails are placed in front of the wind-mill 

 carriage. This operation is repeated every twelve furrows. 

 Two men are, therefore, necessary for the management of 

 the plant, one for the plough and the horse, and one for 

 the wind-mill. The addition of a second cable and drum 

 revolving at a greater speed to haul the plough back would 

 complicate the machine uselessly, although machines are 

 made with the extra attachments. 



The headlands can be easily ploughed, as the cable can 

 haul in any direction, but, in this case, wedges must be 

 placed under the wheels to enable the machine to resist the 

 side strain. 



Shifting the motor from one block to another. When the 

 ploughing of a block is finished, it is easy to shift the motor 

 to another by using it as a self-moving motor. In this case 

 the plough is hauled by the horse in the desired direction, 

 and placed as if about to open a furrow ; the drum is then 

 thrown into gear, and, when the cable starts to wind, as the 

 wheels are not wedged, the latter, offering the least resist- 

 ance, travels towards the plough at a speed of 16 inches per 

 second. It is not necessary to attain a greater speed, as the 

 rails have to be displaced every 20 feet. 



Stability. When the motor hauls the plough in a direc- 

 tion perpendicular to that of the rails, its weight (5 tons 

 18 cwt. to 6 tons 17 cwt.) suffices to secure the required 

 stability, as the flanges of the rolled joist girders serve, at the 

 same time, as anchors in the ground and blocks against the 

 wheels ; when the direction becomes oblique it suffices tc 

 block two of the wheels with pegs. It results from calcu- 

 lations made on this machine, that if we assume the motor 

 with all its vanes, and arrested by the brake (the most 

 unfavorable case), the pressure of the wind should attain 

 5 Ibs. per square yard, that is to say, a rate of 59 feet per 



6279. M 



