320
Molesworth’s pocket-book
Telegraph Construction, by R. S. Brough—
continued.
If the stay be applied above x at a height y'
from the ground, then 2 (p) will have a moment
| = 2 Qo) X-1 about the place of applica-
tion of the stay, tending to bulge the post below
that point.
The stay should be always fixed in the vertical
plane in which the resultant strain acts. If the
resultant strain in one direction be 2 Q>), and the
resultant strain in another direction be 2 (7)
making an angle a with the former direction, and
R be the whole resultant strain, the direction of
which makes an angle ß with the first direction,
then R2 = { 2 (p) } 2 + { 5 (7) } 2 + 2 { 2 O) }
{ 5 (</) } cos. a; and sin. ß = sin. a-
§ v. Pressure of Wind and Water.
If tlie pressure on a flat surface of unit length
and width a at right angles to the current be P, tho
pressure on a surface whose section is a right tri-
p
angle on the same base «.is = 5-, and the pressure
£a
on a surface whose section is semicircular cn
the same base a is = | P; but practically in
the last case the resistance has been found to bø
about = f P.
A fairly safe maximum wind pressure to bo
allowed for is 50 lbs. on the square foot.