LOGGING IN THE DOUGLAS FIR REGION. 87 
metrically around a center core, the strands consisting of wires 
twisted together symmetrically according to a definite geometrical 
arrangement. The unit of construction is the strand. While a 
large number of geometrical combinations are possible, the ordinary 
practice is to use 1 wire in the center of the strand and to surround 
it with 6 wires, then sucessively with layers of 12, 18,- 24, and 36 
wires, etc., the construction being known as the concentric strand. 
Six wires around a center wire produce a strand for a haulage rope. 
A supplementary layer of 12 wires makes a 19-wire strand for a 
hoisting rope. This strand in turn, when covered by a third layer 
of 18 wires, makes a 37-wire strand that is used in a special flexible 
hoisting rope. In strands of uniform diameter the greater the 
number of wires in the strand the more flexible the rope. The 
strands, usually 6 in number, are, as a rule, laid together around a 
hemp center. 
The " haulage rope," 6 strands of 7 wires each, is a relatively 
stiff rope with large wires capable of resisting external wear. Its 
use is limited to conditions where there is much abrasion and little 
bending around sheaves. In the "hoisting rope," 6 strands of 19 
wires each, the wires are smaller than those in a 6 by 7 rope, and 
are less able to resist abrasion, but can more easily be bent around 
sheaves and drums. The "special pliable rope," 6 strands of 37 
wires each, is composed of still smaller wires than the 6 by 19, 
possesses greater flexibility, and may be bent around fairly small 
sheaves. It should not be subjected to much external wear, par- 
ticularly in the smaller sizes, as the wires will be worn off quickly. 
The " extra pliable rope," 8 strands of 19 wires each, is more flexible 
than the 6 by 19, and may be used over smaller sheaves than the 
latter. It is about as flexible as 6 by 37 construction, but not so 
strong, owing to its larger hemp center. 
The ropes so far referred to are of the one-size-wire construction. 
In the making of 6 by 19 rope certain features result from a slight 
modification of the strands and wires. In Seale construction the 
center wire of the strand is large, the next layer of 9 wires is 
small, and the outer layer of 9 wires large. These strands pro- 
duce a rope somewhat stiffer than ordinary 6 by 19 construction 
and having a limited number of uses. The strands of another con- 
struction consist of wires of three different sizes, 7 inside wires of 
uniform diameter surrounded by 12 wires which are alternately 
large and small. This combination increases the metallic area and 
strength by approximately 10 per cent. 
There are two general methods of laying up rope — the common 
type, known as regular lay, and Lang's lay. In the former the wires 
are twisted in one direction and the strands are laid into the rope 
in the opposite direction. Most of the rope made in America is 
