361
OF ENGINEERING FORMULÆ.
Stkains on Telegraph Wise. (Indian Telegraph Dept.)
Applicable to Indian Wire Specification of 1872.
Wires made on tins specification have been used in Japan,
New Zealand, Australia, Cape, and South America.
Constant strength of iron wire = 6000 yards of itself.
„ „ steel „ = 18000 „ „
With a dip of 30 inches per 100 yards span the constant
working strain at the insulator — 1500 yards, or approxi-
mately f'ths of its freight per mile.
The strain varies directly in proportion to the dip.
WITH THE POINTS OF SUPPORT AT THE SAME LEVEL.
S = Span, or length between supports.
D = Dip of the wire.
L = Length of the curve between supports.
T = Strain at the insulator.
t = Strain at the lowest point of the curve.
w = Weight of a uuit of wire.
w.
21S3
w = working strain of wire.
WITH SLPPORTS AT UNEQUAL LEVELS.
x = Horizontal distance from the lowest point of the curve
to the lower support.
y = Ditto ditto to the higher support.
a = Difference in level of supports.