18 ROYAL SOCIETY OF CANADA 



I had hoped to have read before this section a paper giving an account 

 of an investigation as to the effect of the presence of moisture upon the 

 strength of timber. I have, however, been unable to complete the 

 experiments and have been compelled to postpone the j)reparation of the 

 paper for the present, but I wish to conclude this address by laying 

 before you the general results which have been obtained. 



In a paper read before the Canadian Societj^ of Civil Engineers in 

 1895, I dealt with the transverse, compressive, tensile and shearing 

 strengths of various Canadian timbers, but I refrained from referring 

 specially to the effect of moisture, for the reason that 1 was not prepared 

 to accept the general statement, that the strength of timber is materially 

 inci-eased by drying the timber until the whole of the moisture has been 

 removed. It is certainh' true and has been long known, that the com- 

 pressive strength of timber under a steady load is increased — sometimes 

 to an extraordinary extent — by eUminating the moisture, and, it has been 

 assumed, that the tensile, shearing and transverse strengths arc also 

 increased, though perhaps to a less extent, the opinion being based, 

 mainly, I beUeve, on the results of experiments in compression. There 

 are a large number of data as to the compressive strength of ditîerent 

 timbers, but they are, with some exceptions, of little value, as they are 

 not accompanied by information, which is absolutely necessary for 

 the purpose of comparison. Thus, it is not stated whether the speci- 

 mens between which the comparison is made, were in the same con- 

 tinuous line parallel to the axis in the timber from which they were 

 originally cut, a very important factor, as the co-efficients of elasticity 

 and the ultimate strength depend essentially upon the position of the 

 specimen relatively to the heart. As an example of this, it may be 

 stated, that the variation in the direct compressive strength of a Douglas 

 Fir stick was found to be from 2600 lbs. per square inch, near the heart, to 

 6000 lbs. per square inch, ten inches from the heart. The tensile strength 

 of specimens of the same stick was also found to vary in a like manner. 



Neither do the data give sufficient information as to the relative 

 amount of moisture present in the specimens, nor does it seem that any 

 notice has been taken of the effect of the extremes of temperature uj)on 

 specimens in abnormally wet or dry conditions. 



With a view to determining .some of the.se points more precisely, I 

 commenced a series of experiments on hemlock, spruce, red i)ine and 

 white pine, great care being taken to ascertain the effect of any abnormal 

 conditions on the elasticity and strength of the timber in question. 



In the observations 1 u.sed an Unwin's recording extensometer reading 

 to the 1/100. 000th of an inch. I had previously found that with slight 

 variations of temperature, the contraction and expansion of the distance 

 rods of this instrument pnjduced serious errors in the readings, errors, in 

 fact, Avhich often vitiated the whole experiment. 



