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TELEGRAPH CONSTRUCTION.
(By R. 8. Bkough, Esq., M.S.T.E., Indian
Telegraph Department.)
§ i. The Wibe.
Let T = breaking strain of the wire; w =
weight of unit of length of the wire; L = length
of itself it can just support -without breaking.
T
Then L = — an absolute length which is constant
to _ '
frtr any the same kind and quality of wire; and
whose numerical value depends only on the unit
of length adopted, For the ordinary soft iron
wire employed in overland telegraphy,* L — 3|
miles.
Let t — working strain of the wire; I — length
of the wire whose weight is equal to its work-
ing strain; and z = factor of ßafety; «o that
i = - and I = -; then I =' - . When z ~ 4,
z Z w ’
I = 4400 feet for soft iron wire.
Cartesian equation to the Catenary, the origin
being at a distance c below the vertex of the
011176 ‘ / X zS
y ~ ~ (e~ +
Approximate equation to the Catenary :
x2 = 2ff (y c) — I (3/ — c)2.
* The strength of wiro is extremely variable, depending
essentially on quality and temper, and it ranges from soft iron
wire, which will carry 3 miles of itself, up to steel pianoforte
wire, which will curry 16 miles of itself.