FiVpLLan Timher^. 29 



mospheric changes is very objectionable. For gunstocks, it 

 should be comparatively light, and capable of taking wood or 

 iron screws without tearing ; when exposed to wet it should 

 not become rough or woolly, it should clean up well when 

 carved or machined, be close grained and of rather a " cheesy "' 

 nature but hard enough to resist ordinary wear and tear with- 

 out " denting." To a certain extent it should have a good 

 figure, but expansion or contraction is fatal ; for most of the 

 minor uses, bending is one of the qualities required. 



In investigating the value of the six Papuan species, they 

 have been subjected to the following mechanical tests : — 



Crossbueaking or Beam Tests. 



All beam tests were made on a four foot span, but the 

 effective span was 45.71 inches, due to the method adopted of 

 applying the load. The central load was spread over a width 

 of 2.29 inches by means of two swivel bearings. The span (the 

 supports also being on swivel bearings) was 48 inches. 



The formula for calculating the '" modulus of rupture '' was: — 

 F = 3/2 X WL'/^/--' 

 Where W = total load required to lireak tlie specimen. 



L' = the effective span. (Clear sp;in minus the distance 

 between the centres of the 

 swivel bearings.) 

 b = the breadth of the test piece, 

 d = the depth of the test piece. 

 The " modulus of elasticity " was obtained by plotting, on 

 squared paper (Fig. 2, Plate XL), the readings taken on a specially 

 designed "Deflectometer,"^ (Fig. 3, Plate XT I.). The formula used 

 for obtaining the " modulus of elasticity " was : — 



E = WL^/4/y^^^S 

 Where W — weight in pounds, producing deflection. 

 L = clear span (48in.). 

 b = breadth of the test piece, 

 d = depth of the test piece. 

 8 = deflection produced by weight W. 



1 This instrument was designed by Professor H. Payne, and made by his assistant in 

 the Engineering' Labatory. It was used for the first time during these tests, and was 

 accurate tliroughout. 



