331 



IV. — Compression Along the Grain. 



Tests were made upon blocks 8 or 12 in. long, cut off 

 the uninjured ends of the beams after they had been broken 

 at the centre. The ends were cut off square in a lathe and 

 the blocks subjected to compression along their length. Fail- 

 ure occurred in every case by the fibres buckling over along 

 a plane inclined to the axis of the block, the greatest slope 

 of this plane being always parallel to the rings. In this 

 test the whole of the fibres of the test piece are subjected 

 to a uniform stress, and the test is regarded by some ex- 

 perimenters as the best test for comparing the strengths of 

 timbers. 



V. — Compression Across the Grain. 



For this test blocks 8 in. long were used and 3 to 4 in. 

 thick. Each block was laid on its side on the table 

 of the testing-machine and subjected to compression by 

 means of a castiron block 4 in. wide, reaching 

 across the whole width of the specimen. There is 

 no definite stress at which failure occurs in tests of 

 this nature, and the general method is to record the 

 stress at which the iron block crushes into the wood — first 

 to an amount of 3 per cent., and secondly to an amount of 

 15 per cent, of the depth of the specimen. 



Fig. 3. 

 Apparatus for Measuring in Cross-compression Tests. 



For this purpose the apparatus illustrated in fig. 3 was 

 devised. AD is a stiff metal arm turning freely about a pin 

 at A, supported on the block G, that rests on the edge of 

 the table. A vertical insulated pin, EF, passes through the 

 middle of the arm, being free to move downwards through 

 the arm, but is pressed upwards by a strong spiral spring. 

 It is tipped with platinum at the top, E , and a wire can 

 be attached at F . The pin at A rests beyond the edge of 

 the table ; its centre is on the same horizontal plane as the 

 surface of the table, and also in a straight line with E and 

 three nicks, B, C, D, on the underside of the arm. The dis- 



