Pcqnian Timbers. 31 



Tension Tests. 



Tension tests are not of very great value, as usually timber 

 is stronger in tension than in any other direction, and would 

 seldom fail under that stress while other portions of the same 

 structure, constructed of the same wood and of the same dimen- 

 sions, were directly under any of the other stresses. In very 

 brittle timber, it might happen, but never in sound, fibrous 

 wood. For comparison, however, it is well that these tests 

 should be made. 



The " tension " specimens were prepared in the lathe in the 

 form shown in Fig. 4. The original dimensions were 20 inches 

 long and 2J inches square. These were turned to a diameter 

 of f inch in the centre, parallel for eight inches between the 

 shoulders. The portion to be gripped in the testing machine 

 was 3J inches by 1 3-8th inches diameter, the remainder being 

 just cleaned up. The experiments and remarks are given in 

 the schedule of details. The mean breaking strengths per 

 square inch are given in Table 4. 



Shearing Tests. 



Specimens cut from the compression pieces were tested in 

 shear. They were approxima*tely three inches square and one 

 and a-half inches deep, the depth being along the grain. They 

 were tested in double shear. Half of the pieces were sheared 

 parallel to the annual rings and the other half at right angles 

 to them. The shearing strength was calculated by dividing 

 the load producing shear by the area sheared. Thus — weight 

 per square inch = Total load/2bd. 



