OF ARTS AND SCIENCES. 315 



Conclusions. 



The conclusions which may be drawn from the research here 

 described, the writer considers to be as follows: — 



That for spruce beams of small section, selected from lumber which 

 has been moderately well seasoned and dried, the strength is not 

 materially increased by the timber being kiln dried ; that the modulus 

 of elasticity is not proportional to the modulus of rupture ; and that 

 the elasticity is not increased by kiln-drying the timber. 



That with small spruce beams those which have the greatest 

 strength bend the most before breaking. 



That when a load between h and J of the so-called breaking weight 

 is applied to a small spruce beam it produces a deflection which for a 

 few hours rapidly increases, until the beam has fairly settled under its 

 load ; from this time the deflection increases gradually uutil a short 

 time before breaking, when it increases more and more rapidly. 



That a load of ^ of the so-called breaking weight if applied but for 

 a few days does not injure such beams. 



That a load which will cause such a beam to deflect one half of its 

 maximum deflection before breaking will ultimately break the beam. 



That under the most perfect conditions small spruce beams will 

 not permanently support a load of one half their so-called breaking 

 weight. 



That the position of the annular rings in spruce beams of small 

 section materially afPects the strength of the beams, their strength 

 being the least when the rings make an angle of 45° with the top 

 and bottom surfaces of the beam. 



The writer agrees with Prof. R. H. Thurston in considering 5 as 

 the least factor of safety which should be used for wooden beams 

 under an absolutely static load. 



