i 5 4 ROUND THE YEAR 



theoretical solution. I do not venture to accept the 

 challenge, but shall merely look about to see whether 

 some particular cases, artificially simplified by assump- 

 tions, can be illustrated by known results of calculation 

 and experiment 



A joint of the grass-haulm is usually a hollow 

 cylinder. What is the advantage derived from this 

 form ? A column of circular section is particularly 

 appropriate to a structure which has to resist pressure 

 from all sides. Such a column may be either a solid 

 or a hollow cylinder. Of these two the hollow cylinder 

 is clearly the stronger for a given sectional area. This 

 becomes evident when we consider what will happen 

 during bending. One side (the convex side) will be 

 stretched ; the opposite side will be compressed, 

 and between the two there will be a neutral line, 

 where there is neither extension nor compression. 

 Material lying close to the neutral line would be less 

 useful, and would stiffen the cylinder more if it 

 were removed and disposed uniformly on the outside 

 of the rod where the extension and compression are 

 greatest. A hollow cylinder is inevitably stronger to 

 resist bending than a solid cylinder of the same weight 

 per foot run. 



The joints of the haulm get narrower in regular 

 succession upwards, the long joint which carries the 

 spikelets being conical and usually very slender. 

 This is attended with various advantages. The 

 moment of the load varies with the distance, and 

 is least at the summit of the stalk. Hence economy 

 of material is obtained by a reduction of thickness at 

 that point. The surface exposed to wind is reduced 



