AERIAL TRAMWAYS 
257 
be lifted several feet above ground by tightening the secondary- 
cable with a few turns on the drum. The logs were attached by 
chokers to a traveling block that ran on the main cable. The 
load descended by gravity, its speed being controlled by a |-inch 
cable which was attached to the rear of the traveling block, 
and then passed through a block fastened to the tail tree and thence 
down the slope to a drum on the engine. The trip line was held 
Fig. 81. — A Single-wire Tramway used in the Northwest. The details of 
the trolley and the method of attaching logs to it are shown in the en- 
larged cut. 
in position by several blocks placed at suitable intervals on the 
slope. This line also served to return the block to the head of 
the tramway. In case of a break in the machinery or of the load 
becoming unmanageable the main cable could be dropped to 
the ground and the load stopped. 
A system of this character may be used for distances of 3000 
feet when there are no pronounced elevations between the two 
ends of the tram. 
Logs containing from 5000 to 6000 board feet have been success- 
fully handled. The hourly capacity of this tramway was 
12,000 board feet, when the logs averaged from 300 to 500 feet. 
Three men were required to operate the tram. 
A single-wire gravity tram way ^ used in the West had a Ig-inch 
main cable 2100 feet long suspended between a tree on the upper 
slope and one at the base of the grade, as shown in Fig. 82. Auto- 
matic trips were placed on the main cable at the loading and 
1 See The Timberman, April, 1912. 
