PLOWS FOR MECHANICAL POWER 171 



the plow points may be raised from five to twelve inches on 

 different makes. Castered wheels on one type make it easily 

 possible to trail several sections one behind the other for 

 passage through narrow openings. 



Since in these rigid gangs the bottoms are held rigidly, irregu- 

 larities of the ground surface cause the furrows to be of 

 uneven depth, some plows running deep and others skimming 

 or skipping entirely. An obstruction before one plow lifts 

 several out at one time, and an accident to one may put the 

 entire set out of commission. For these reasons the smaller 

 sizes of three to five bottoms are more popular than the larger, 

 even though the latter are more compact. On one type each 

 bottom is held in place by a device which allows it to be thrown 

 upward without damage in case it strikes a stone or root. 

 While in service, however, the bottoms are prevented from 

 adapting themselves to uneven surfaces. 



For small tractors solid gangs of lighter construction and 

 adapted to either horse or engine hitch are often used singly. 

 For larger engines it is necessary to combine several plow units. 

 Cables, rods, and chains are used to hitch them behind the 

 engines, the hitch usually being devised to fit the particular 

 case in hand. Where an engine is not equipped with a wide 

 plowing drawbar, it is necessary to attach the cables or chains 

 to a crossbar and thus hitch to the centre of the engine. Since 

 the wheels of each gang must clear those of the one preceding, 

 the combination of from one to four units renders the outfit 

 long and unwieldy. This is especially true if, for the sake 

 of flexibility, small gangs are used. The long cables are apt 

 to become fouled in turning to the right, and in plowing around 

 corners strips between the gangs are usually left unplowed. 

 Castered wheels and a special coupling device on one type are 

 claimed to render the outfit capable of turning in either direc- 

 tion and plowing perfectly around corners, the total width of 

 cut being reduced of course on the turn. 



The practice of combining plow bottoms in a rigid gang has 



