SUBTERRANEAN LINES. 
137 
soldered to the end of these chains, and the vibrations cease to 
be communicated to the chimney. 
Subterranean Lines .—The wires first used in America in the 
original telegraphs were buried in the ground, and were made 
Fig. 78. 
of No. 16 copper wire, covered with cotton and steeped in 
thick tar. These wires, grouped together in cables of three, 
four, or more, were afterwards enclosed in a leaden pipe, which 
was protected externally by tarred rope. At certain intervals, 
the ends of the wires were brought to the surface in cast-iron 
test boxes. The lines through tunnels were constructed in the 
same manner, and were placed in wooden troughs. Mr. 
"Walker was the first to introduce gutta-percha in England, as 
an insulating material for the telegraph wires he laid in the 
