SLEDS AND SLED-IIAULING 
179 
tion devices placed under the rear end of the boiler. Each has 
a heavy steel runner, hung on a 42-inch shaft and equipped on 
each end with a heavy box in which an iron shaft carrying a heavy 
steel sprocket wheel runs. 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 traction 
surface. The weight of the engine is distributed over the sur- 
face of the tread chain by two tool steel roller chains, which 
Fig. 50. — A Lombard Steam Log Hauler. 
run in a tool steel channel attached to the underside of the steel 
runner_ inside of the tread chain. A bearing surface of approxi- 
mately 4^ square feet is given to each tread chain which is suffi- 
cient for tractive purposes and does not tear up the road. 
The boiler, which is equipped with locomotive boiler attach- 
ments, is 15 feet long, 36 inches in diameter and is built for a 
working pressure of 200 pounds. The water tank is placed 
under the boiler directly in front of the fire box and has a capac- 
ity of ten barrels, which will run the hauler for 5 miles. 
The engine has four vertical 6^- by 8-inch cylinders which 
transmit power by a series of gears to the rear sprocket wheel 
on each runner. Two cylinders are placed on each side of the 
