290 



PROCEEDINGS* OF THE AMERICAN ACADEMY 



TABLE in. 



From these experiments I think we may draw the following con- 

 clusions : — 



That the Modulus of Elasticity depends not only upon the elas- 

 ticitj^ of the material, but also upon the length of time the load is 

 applied. 



That when subjected to loads not exceeding one-sixth of the break- 

 ing weight, spruce beams do not take a permanent set. 



That even under very small loads, if applied for any length of time, 

 there will be a temporary set. 



That knots and knarls in beams loaded at the centre, when not 

 within one-eighth of the span of the centre of the beam, do not mate- 

 rially affect the elasticity under small loads. 



That the deflection is very nearly pro])ortional to the load, far 

 beyond the customary limits of strain, and that the Modulus is conse- 

 quently very nearly constant for all moderate deflections. 



That a high Modulus of Elasticity does not always accompany high 

 transverse strength; for, as shown by Table I., piece No. 10, which 

 had the greatest transverse strength, gave next to the lowest value 

 of E. 



That in spruce beams the upper fibres commence to rupture by 

 compression under about four-fifths of the breaking weight, and the 



* Approximately. 



