The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

542 TELEGRAPH INSULATION.
Fig: 31. seen in fig. 31. An auger-hole the size of the
glass is bored through the pole about two
inches from the end. With a chisel the
wood about the auger hole is cut out, which
leaves a mortised opening for the insulator,
as seen in fig. 31. Letter A is the insulator,
with the flange opening; B is the projecting
head; c the groove or hole for the wire, D
one of two small boards nailed on the top
of the pole to form a roof. When trees were
used on the route of the line, a bracket was
attached to the tree, as represented in fig. 32, excepting that
the board roof is not shown in the figure. This insulator
allowed the wire to rend through: so that whenever a tree fell
upon the line, communication was not interrupted. When the
Fig. 02.
wire is first stretched it is taut, but in a short time it becomes
slack by expansion, and whenever a tree falls upon the line
the wire is not broken Bl carried to tle earth with the tree.
If the wire does not. n the moist ea the telegraph continues to work without interruption. If, however, the wire is
imbedded in the earth, communication will be stopped until
the wire is elevated. In forest provinces the open insulator
has been found indispensable. In open countries it has not
been considered of any advantage.