LINE CONSTRUCTION 
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It is also very convenient for stretching a wire at its termina¬ 
tion. 
All these stretchers are made of galvanized iron. 
The wires wound round the drum of double stretchers must 
be joined by a connecting wire, soldered at each end ; and this 
is especially necessary in the case of collar stretchers. 
Construction of Telegraph Lines .—The preliminary step to 
the construction of every telegraph line is the selection of the 
best route. 
If the line has to be made where there is no network of 
railways, the different directions that seem to offer most 
advantages are compared as to cost and facility of maintenance 
and working. 
When the route has been fixed upon, the materials are sent 
out. On railways the carriage is effected without expense, for 
stores are collected at the principal stations on the line, and 
are afterwards carried where required on small trucks pushed 
along the rails by the workmen. This operation can, however, 
only be carried on at certain times of the day, on account of 
the passing trains. It is sometimes even found, on single 
lines of rails, more advantageous to have the poles carried by 
the men over a great part of the course. 
Where there are no railways, the materials are usually 
distributed by traction engines, or carriers are hired to convey 
them along the ordinary roads. 
The details are thus laid down :— 
The vertical distance between two wires placed on the same 
side of a pole is 2 feet. This interval is reduced to 20 inches, 
or even to 16 inches, at places where the lines cross roads or 
highways. The insulators attached to one side of the poles are 
placed in the middle of the spaces between those attached to 
the other side. These data give the means of calculating the 
height of poles required for a given number of wires. The 
height of the lower wire from the ground, at the middle of its 
span, must be at least 6 feet 6 inches along railways, 10 feet 
along ordinary roads, and 15 feet where a road frequented by 
loaded waggons is traversed. 
In certain cases where the line must cross the road, the 
insulators are fastened to a horizontal beam, placed on poles 
planted on each side of the road, and sufficiently high to allow 
