SLEDS AND SLED-HAULING 



173 



driving gear on geared locomotives, substituting for driving 

 wheels a special form of heavy traction device. 



The essential features of the hauler are a locomotive-type 

 boiler mounted on a heavy reinforced channel-iron frame, which 

 also supports the cab and coal tender at the rear. The machine 

 is supported in front on a narrow tread sled, which is so con- 

 structed that it may be run either forward or backward. A pilot, 

 who sits on the front of the machine, steers the hauler by means 

 of this sled. 



A Luinburd SLL-a.ni Lo'j, Hauler. 



The weight of the machine rests chiefly on two special traction 

 devices placed under the rear end of the boiler. Each consists 

 of a heavy steel runner, hung on a 4|-inch shaft and equipped on 

 each end with a heavy box in which runs an iron shaft carrying 

 a heavy steel sprocket wheel. Each set of sprocket wheels 

 meshes into and carries an endless tread chain 12 inches wide 

 and 14 feet long, which is armed with calks and furnishes the 

 tractive surface. The weight of the engine is distributed over 

 the surface of the tread chain by two tool steel roller chains, which 



