TESTS OF ROCKY MOUNTAIN WOODS FOR TELEPHONE POLES. 25 
lodgepole pine shipment averaged about 22 per cent moisture, 
though the outer shell of the poles was somewhat drier (see, fig. 3) . 
This would tend to make the difference between the strength of the 
poles and the actual strength of the material in it much greater than 
was the case. The curve given on page 10 of Forest Service Circular 
108, The Strength of Wood as Influenced by Moisture, shows that, 
for eastern spruce, strength in bending will be reduced by about 30 
per cent when the moisture content is increased from 8 per cent to 
16 per cent. Tests on lodgepole pine from Wyoming indicate a 
reduction, under similar circumstances, of about 25 per cent. The 
curves shown in figure 8 have, however, been plotted with the values 
as obtained from the tests. 
The curves, arranged in order of the modulus of rupture of the 
poles from highest to lowest, show the relation between the modulus 
of rupture of the small, clear sticks and the fiber stress of the poles 
at the elastic limit and maximum load. The position and number 
of checks, knots, and other defects, rather than the quality of the 
clear wood, determines the grade of a pole. While the curve for 
the modulus of rupture of the small pieces is erratic, as would be 
expected from the rather small number of tests averaged for each 
pole, it shows a tendency to fall with a fall in strength of the poles, 
indicating the influence of the quality of the clear wood on the 
strength of the poles. The most important relation shown by the 
curves is that the ratios between pole and minor strengths are not 
the same for the different species, indicating that it is not safe to 
compare species for use as poles on the basis of the strength of their 
clear material. For example, western red cedar gave an average 
modulus of rupture for the small, clear beams of 9,305 pounds per 
square inch, and the lodgepole pine from Montana averaged 12,775. 
While the strength of the clear material of the pine is thus 37 per 
cent higher than that of the cedar, the average strength of the poles 
was a little less than 12 per cent higher. The ratios of the average 
modulus of rupture of the poles to that of the clear material for two 
. conditions of moisture is as follows : 
Kind of poles. 
As tested 
at 8 per 
cent. 
As esti- 
mated 1 at 
16 per cent. 
Western red cedar 
0.74 
.60 
.60 
.48 
0.98 
Lodgepole pine: 
Green cut 
.80 
Fire killed 
.80 
Engelmann spruce, fire killed 
.65 
1 On the basis that an increase in moisture from 8 to 16 per cent causes a 25 per cent reduction in strength. 
