288 PEOCEEDINGS OP THE AMERICAN ACADEMY 



which was allowed to remain upon the beam for about two hours, the 

 deflection being measured directly after the weight was applied and 

 just before it was removed. The beam was then allowed a certain 

 time to recover its set. In two cases, the beams, after having been 

 subjected to a load of 100 lbs., finally returned to their original posi- 

 tion, and it appeared probable that all would have done so had sufficient 

 time been allowed for the purpose. 



After the piece had nearly recovered from the effects of the load 

 of 100 lbs., a load of 150 lbs. was put on the beam, and gradually 

 increased until the breaking point was reached. 



The remaining pieces were tested with a load of 100 lbs. in the 

 same way, and then subjected to a load of 400 lbs. for one or two 

 minutes, for the purpose of getting the deflection under that load, 

 and immediately after subjected to the full load of 500 lbs., which 

 was gradually increased until the piece broke. As the load approached 

 the breaking weight, it was increased by the addition of only one or two 

 pounds at a time, so that the breaking weight could be obtained with 

 sufficient accuracy. In fact, the breaking weight is so much modified 

 by the time occupied in breaking the beam, that it is difficult to ascer- 

 tain exactly what it really is. For any load, over three-fourths of 

 what is called the breaking weight would probably break the beam 

 if applied long enough. 



Table I. gives the values of the Modulus of Rupture of each piece, 



3 Wl 

 computed by the formula H z=i- 'jri~,, in which JR denotes the Mod- 



ulus of Rupture ; W the breaking weight of the beam, and the other 

 letters have the same significance as in the formula for E. The load 

 which would break a beam of the same wood, one inch square and 

 one foot between supports, if applied at the centre, is also given 

 in the same table. This load is one eighteenth of the Modulus of 

 Rupture. 



When the weight of 400 lbs. was applied to piece No. 7, it imme- 

 diately cracked at a knarl in one of the lower edges, about three- 

 fourths of an inch from the centre of the beam. As it was thought 

 that the beam would soon break entirely, the load of 400 lbs. was 

 allowed to remain on the beam ; but at the end of one hundred hours 

 tlie deflection had only increased 0.2224 inches, and as it was evident 

 that it would, at that rate, take a long time for the beam to break, the 

 load was then gradually increased until the piece broke at 550 lbs., 

 giving a Modulus of Rupture considerably above the average. It was 

 noticed in this beam that the deflections under the loads above 500 



