224 NOTICES OF AUTHORS. 



across in detail. In like manner, when the direct 

 longitudinal strength is tested, the external circles be- 

 ing in greater tension than the internal, the tightest 

 parts of the log will give way in succession, like a 

 rope T^ith strands of different degrees of tightness ; 

 yet the lateral adliesion of the layers will have con- 

 siderable effect in strengthening the mass. 



The above explains the fallacy of estimating the 

 longitudinal strength of a thick piece of timber from 

 experiments vdth. small shreds ; it likemse explains 

 how a large unbuilt mast is so easily sprung ; where- 

 fore a beam round as grown will be rendered stronger 

 as a beam by being formed into a hollow cyHnder, 

 by boring out the central part ; and also how a 

 square log will be strengthened as a beam, by cleav- 

 ing it up the middle, and placing the two pieces on 

 edge, with their outside or backs together. In the 

 latter case, the middle, by being tm*ned outside, and 

 exposed to the air, will contract more than what it 

 would do shut up and covered by the exterior wood, 

 especially if resinous pine timber, which continues 

 to contract for many years, owing to the resin, when 

 exposed to the au*, gradually drying or undergoing 

 some change, by which it is diminished in size, and 

 rendered similar to amber» 



