104 POWER AND THE PLOW 



of hitch. This is done either by a vertically swinging rod 

 or a series of holes in an upright beam. 



SPECIAL TYPES 



For overcoming the disadvantage of the tractor in extremely 

 soft ground, no device appears to be more successful than the 

 substitution of a caterpillar tread for the ordinary round 

 traction wheel. Although the idea is several generations old, 

 a tractor with this type of transmission has only recently been 

 put on the market in large numbers. The weight of the tractor 

 is supported on steel rollers, which run upon the inside of a 

 continuous belt made of pressed steel plates. The belt is 

 driven by a sprocket and chain, so that the tractor virtually 

 lays its own track and picks it up again. A single wheel in 

 front supports part of the weight of the tractor at rest. Under 

 working conditions, practically all the weight of the tractor 

 is borne on the rear, where it is distributed over such an area 

 as to reduce it to seven or eight pounds per square inch. Steer- 

 ing is done by driving the caterpillar webs independently of 

 each other, a slight amount of flexibility in the joints allowing 

 them to turn sidewise. The power is transmitted by a line 

 shaft connected to the crankshaft by a multiple disk clutch. 

 The connection is semi-flexible so that the bevel pinion on the 

 end of the shaft may be shifted to engage a smaller driving 

 gear for a change of speed. Two bevel driving gears are con- 

 nected to the countershaft by independent friction clutches 

 in order to accomplish the forward and reverse motions. 

 This tractor will work in many sections where the round- wheeled 

 tractor is impracticable, but the natural wear on the many 

 joints and the difficulty in turning the outfit are disadvantages 

 which accompany high tractive efficiency. Power in this 

 tractor is supplied by a high-speed four-cylinder four-cycle 

 verticle engine set lengthwise of the frame. 



A light tractor on the order of a motor truck, but adapted 



