854 REPORT—1885. 
The specifications for telegraph poles, in addition to quoting dimen- 
sions, prescribe that they are to be winter felled, sound and hard grown 
(.e., well-hearted, with the annual rings closely pitched), straight, free 
from large or dead knots and other defects, to have the bark completely 
removed, and to contain the natural butt of the tree. They are usually 
from 5 to 6 inches in diameter at the top, and they grow with a taper 
that accords satisfactorily with the theoretical law that should give the 
greatest strength at each section of their length. 
No systematic inquiry has, as far as I am aware, been made into the 
mechanical properties of Scandinavian red fir in its native or unhewn 
state, though at different times isolated experiments have been made on 
its resistance to flexure. 
The immense growth of the telegraph system in this country, the 
increased utilisation of public highways with their bends and curves, the 
wind pressures arising from the rapid multiplication of wires, have forced 
closer attention to the stresses applied, and to the more scientific bearing 
of the question. The selection of the proper scantling has been very 
much a rule of thumb process, but stability has been obtained by struts, 
stays, and double poles framed together. Subsequent experiments have, 
however, shown that practical experience has not erred in specifying 
dimensions. 
As considerable doubt existed as to whether constants obtained from 
square timber could be accurately applied in calculating the strength of 
naturally grown trees, in which the annual rings of growth were un- 
severed, it was determined by the Post Office authorities to make careful 
and accurate measurements of the strength of the poles actually used, and 
a substantial testing apparatus was constructed for the purpose. A stout 
wrought-iron cylinder, 14 inches in diameter and 6 feet long, was rigidly 
held down on a suitable framing by two 2-inch tie rods. The butt of the 
pole to be tested was placed inside this cylinder to a depth of 5 feet 
6 inches, carefully packed all round, and tightly rammed with gravel to 
represent the conditions when in use. It was then placed horizontally, a 
scale pan was suspended from what would be the resultant point of a line 
of wires at the further end of the pole, and weights were added until the 
pole broke. An oak plank or saddle distributed the load as would be the 
case on an actual line of telegraph. 
Table No. I. contains the results of the experiments made upon ten 
comparatively newly creosoted poles. 
This gives a mean constant with formula 2 of 1,337, that obtained 
from the seven stout poles alone being 1,302, and from the three light 
poles 1,417. 
As the investigation referred primarily to lines built with stout poles, 
1,302 is the value used in calculating subsequent tables. 
Table No. II. contains the results of similar experiments made upon 
six old poles creosoted fifteen years ago, and upon three uncreosoted 
poles imported in 1884, the constants being 1,276 and 1,232 respectively. 
As previously stated, formula 2 is really derived from experiments 
made on square timber, a multiplier being used to reduce results when 
round timber is in question. But obviously the strength of round 
timber varies as the cube of the diameter, so a constant has been obtained 
for the formula 
D3 
w= K “2 . . : . . ° . (3) 
