166 Proceedings, <&c., for 1884. 



for each main cable, and then to subdivide this into small rec- 

 tangles by means of the several bundles of wires of which the 

 main cable is composed. Each of these small sections would be 

 supplied by the individual wires of the bundles. 



March 26th, 1884. 



Mr. G. R. B. Steane read a paper on tl Timber." 



A piece of timber may fail, in many ways, e.g., by tension, 

 detrusion, shearing, direct crushing, as in a short block ; crushing 

 and flexure, as in struts of medium length ; and pure flexure, as in 

 long columns. 



It is essential that we should know the limits of strength and 

 elasticity. Up to the elastic limit it is found that the elasticity is 

 approximately equal in tension and compression, but beyond that 

 limit this is no longer the case. This is probably the reason of 

 the very remarkable behaviour of beams of every material when 

 approaching their breaking load. 



In the conduct of experiments on timber but little care is usually 

 bestowed on the selection of suitable pieces for testing*. The pieces 

 tested are usually of small size, and in this case the various 

 apparent strengths are invariably too high. 



With regard to factors of safety, the question, arises, "Should 

 we use the same factor for all timber structures, as some writers 

 seem to imply?" He thought not, for some timbers are more 

 reliable than others, and it is only by numerous and very careful 

 observations on the behaviour of any kind of timber that we can 

 come to any satisfactory determination of its proper factor of 



In the discussion which followed Mr. Steane's paper arose the 

 important question of cheap flood-openings. 



The ordinary culverts and small timber bridges to be seen in 

 the colonies show great diversity of practice. 



In one of the colonies the bridges for a single line narrow-gauge 

 railway are 1 5 feet wide, and decked all across ; and one rather 

 important bridge has an open space in the centre, and is decked 

 at the sides. 



Timber railway bridges should never be built on the skew ; for, 

 in that case, part of the weight of the engine comes on a rigid pile, 

 and another part on a yielding beam, causing the engine to roll. 



A very cheap form is that used on the Victorian light lines, 

 10 or 11 feet spans, with planks 7 inches square section, going 

 over two spans and breaking joint over each. Ballast is laid over 

 the whole deck, and sleepers put on it as on the earth formation. 



