''1 rigidity, ini.l thus exerts a rniitinually IIK reusing resistance, O 

 that there is produced a more or le-> perlo'i <:.|uali/aiion of HtrrM 

 IhrOUgbmi the (onion .>!' the beam under , . nu'i-eMtion, nnd this equal- 

 i/:itioii will doubtless materially a Meet botli the ehmticity and the 



rtnagth, 



An iiitenv^iing PUJHT mi the siirfaee- loading of beams was presented 

 by Prnl'. ( '. A. ('ariis- Wilson to ;!ie 1'hy-ical Society of London, (Kn-), 

 and an abstract of thi^ l'at -i i- to be found in the author's treatise on 

 Theory of Structures. 



The co-efficient of elasticity, :is determined by the tranverse loading, 

 i> di-diieed from the formula 



1 AH-" /. 



=T ID- bd 



W being the iucrement of weight corresponding to the increment 

 .\ Dof the deflection. 



Here again an error i d in the estimated depth will produce an 

 error J E in the calculated co-efficient of elasticity measured by 



A =3 * Arf. 



DOUGLAS FIR. 



Heanis I to III were sent to the Testing Laboratory by Mr. John Ken- 

 nedy, Chief Engineer of the Montreal Harbour Works. 



Beams I and II were of good average quality. 



Beam I was tested on March 1st, 1893, with the annular rings as in 

 l-'ig- .'!. The load was gradually increased until it amounted to 45,COO 

 His., when the beam failed by the tearing apart of the fibres on the ten- 

 sion face. 



The maximum skin stress corresponding to the breaking weight of 

 45,000 Ibs. is 4897 Ibs. per square inch. 



The co-efficient of elasticity, as deduced from an increment in the 

 deflection of .23-in. between the loads of 3500 and 22,500-lbs., is 

 1,138,900 Ibs. 



Table A shows the several readings. 



Beam II was tested on March 2nd, 1893, with the annular rings 

 running as in Fig. 4. 



The load was gradually increased until it amounted to 36. 575 Ibs. 

 when the beam failed by shearing longitudinally. 



I i 



fSOOO J6J7JT 



fig 3 /~,g. 4- frg. 3 



The maximum skin stress corresponding to this breaking weight is 

 4378 Ibs. per square inch. 



In connection with this experiment it is of interest to note that the 

 timber, although it had failed by longitudinal shear, still posse.- 

 very large amount of transverse strength, and similar facts will be 

 subsequently referred to in the case of other beams. After the frac- 

 ture, the load upon the beam was again gradually increased to 34,000 

 Ibs. before a second failure occurred. 



The <o-efficient of elasticity, as determined by the iucrement in the 

 deflection of .1 in. between the loads 2000 and 18,000-lbs., is 

 1,14G,-900 Ibs. 



Table B shows the several readings. 



Beam III was tested on March 2nd, 1893, with the annular rings 

 :i- in Fig. 5. 



This Beam was of especially excellent quality, with clear, close, 

 parallel L'rain, perfectly sound and free from kuots. 



5 



