On the strength of Pine and Spruce Timber. 





Table (D.) Relative stiffness of White Pine, Spruce and Southern Pine, at dif- 

 ferent deflexions, White Pine at each particnlar deflexion beins; taken as unit. 



RATIOS OF STIFFNESS. 



— a +1 



G c -P 



<U o g 



^ r ° 



6 



s 



> 



Spruce. 



6 



a 



a 



o 



1.801 



i 



3 2 



i. 



1.107 



1 



4 1) 



i. 



1.148 



1.512 



_2_ 

 4 



i. 



1.0S6 



1.493 



3 



4 



i. 



1.087 



1.514 



4 



i. 



1.098 



1.522 



5 



4 



!. 



1.078 



1.532 



C 

 4 



1. 



1.056 



1.465 



7 

 4 



1. 



1.096 



1.543 



S 



4 



1. 



1.102 



1.652 





 40 



1. 



1.110 



1.729 



A! 

 4 



1. 



1.107 



1.761 



1 I 



1 40 



1. 



1.111 



1.807 



Observations on the foregoing Tables. 



Although table (B) embodies all the information given in table 

 (A), it is nevertheless thought of some importance to present the re- 

 sults actually obtained in the experiments, the mind is thereby better 

 satisfied, and in this instance the general agreement of those results 

 will tend to inspire confidence. Table (C) contains the average of 

 the results of the original experiments under that head, which were 

 found to harmonize with each other in the same general manner as 

 those of table (A). It may be remarked with reference to the weight 

 producing fracture, that the results given in table (C) are slightly 

 overrated in consequence of the small time occupied in making the 

 experiments ; this, however, is no practical disadvantage, as in cal- 

 culating the strength of timber from algebraical formulae, large al- 

 lowance must always be made to provide against accidental defects. 



It was observed in all these experiments, that the failures of the 

 wood began at the top. The upper fibres, for rather less than half 

 the depth of the beam, were gradually crushed and broken off in the 

 bending of the specimen, and at last when no more weight could be 

 supported, a fracture suddenly took place, the lower fibres being 

 drawn asunder. It seemed that the bending took place more in con- 

 sequence of the crushing of the iinner fibres than the extension of 



