312 



PROCEEDINGS OF THE AMERICAN ACADEMY 



TABLE IX. 



Deflection of Piece No. 7, Series No. 3, tinder a Load of 401 lbs. or 

 § of its Calculated Breaking Weight. 



Having proved that § of the so-called breaking weight of a beam 

 is more than it will carry permanently, the next beam was subjected 

 to only ^ of its calculated breaking weight. 



This load was kept on the beam 49 days, during which time the 

 deflection increased from 13.4 mm. (0.527 in.) to 18.55 mm. 

 (0.73 in.) It was then necessary to remove the beam from the 

 machine, that the latter might be used for other tests. The " set " of 

 the beam on the removal of the load was 4.35 mm. (0.171 in.). 



Seven days after the load was removed it was again put on the 

 beam, and allowed to remaia 77 days, when it was again removed, 

 that the beam might be put on a temporary frame and kept there, 

 with the same load suspended from it, until it broke. 



The " set " of the beam on the second removal was only 3.76 mm. 

 (0.148 in.), being less than what it was after the first removal. 



The deflections of the beam are given in Table X. 



As this beam continued constantly to deflect, and as this increase in 

 deflection is still going on, it seems to the writer that it must ulti- 

 mately break under this load, for when the deflection reaches a cer- 

 tain limit it will, as is shown by the other pieces, rapidly increase 

 until it breaks. 



Observations on Tables I., II., and III. Comparing Tables II. 

 and III., we find a great difference in the values of the moduli of 

 rupture for the two sets of experiments, although the planks from 

 which the pieces were cut were selected from the same lot of lumber 

 and dried the same length of time. 



