230 On the strensrth of Pine and Spruce Timber. 



the load was immediately removed from the platform, a new speci- 

 men substituted, the index readjusted to the zero of the scale, and 

 the same operations repeated. By this method the number of useful 

 observations during each trial, was greatly augmented without causing 

 any additional trouble. 



From the foregoing description, it will be seen that the loads were 

 not allowed much time to act upon the beams, from which it follows 

 that the weights producing the different deflexions are rather over- 

 rated. With regard to the object for which these trials were insti- 

 tuted, this was a matter of no importance, as it could not affect the 

 relation between the different kinds of wood, and upon making some 

 experiments to ascertain the amount of error, it was found so small 

 that it might with safety be neglected. 



In the first trial, for instance, (specimen, No. 1, Table [A,] the 

 load of 2662 pounds, which produced a deflexion of ^^th of an inch 

 to a foot, instead of being immediately removed, was allowed to re- 

 main suspended for two hours and forty minutes, when it was found 

 that the center of the beam had sunk only 0.077 of an inch. 



The foregoing observations, with a few explanatory remarks, will, 

 it is hoped, render the following tables intelligible. 



Table (A.) Detailed Statement of Experiments to determine the relative Stiff- 

 ness of White Pifne, Spruce and Southern Pine. 



KE MARKS. 



Whole length of 

 specimens in feet 9.389 



Bearing length in 



.1 



7. 



2.75 

 5.5 

 each 



feet 



3readth in inches 

 Depth in inches 



In these trials 

 specimen, upon being re- 

 lieved of the load pro- 

 ducing the greatest de- 

 flexion, sprung back by 

 the elasticity of the wood 

 until the center came 

 within about 0.046 inch- 

 es of being as high as it 

 was before the experi- 

 ment commenced. This 

 deflexion of 0.046 inch- 

 es, would have been still 

 further reduced had more 

 time been allowed. 



