OF ARTS AND SCIENCES. 



311 



Series No. 3. 



The results of the second series of experiments convinced the writer 

 that a perfect and dry spruce beam would in time break under a load 

 of only one half of its calculated breaking weight, but to make the 

 results more certain a third series was undertaken, with the same 

 object in view. 



The pieces of wood tested in this series were to all appearance 

 equally as perfect and dry as those in Series No. 2. Table III. gives 

 the dimensions of the beams in this series, the moduli of rupture of 

 the first five pieces, and the ultimate deflection of all the pieces. 



The average value of the modulus of rupture of the first five pieces 

 was taken as the basis from which the breaking weight of pieces 

 Nos. 6, 7, and 8 were computed. 



Piece No. 6 of this series was broken by a load of f of its calcu- 

 lated breaking weight, 22 days after the load was applied. The deflec- 

 tions of this beam at various intervals during the 22 days are given 

 in Table VIU. 



TABLE VIII. 



Deflection of Piece No. 6, Series No. 3, under a Load of 399 lbs. or 

 I OF its Calculated Breaking Weight. 



The next piece of the series, No. 7, was subjected to a load of f of 

 its breaking weight, which it carried 24^ days, and then gave way as 

 the others bad done. 



The deflections are given in Table IX. 



