TIMBER TESTING 293 



homogeneous substance, and not as a natural 

 product, which was once as much a living being, 

 subject to various outside influences, as the 

 experimenter himself. A few trial experiments, 

 with specimens cut from the same board, will 

 show that an experimental beam cannot be 

 regarded in the same light as a bar of steel. 



The late Professor J. B. Johnson, in his 

 "Materials of Construction," attributed the often 

 apparently inexplicable results obtained in 

 timber testing, to the " variations in the per- 

 centage moisture present in the timber," and 

 his work on the subject showed, as far as 

 American woods are concerned, that the strength 

 at 12 per cent moisture was 75 per (Jent greater 

 than when the wood was green. According to 

 this authority, "It is the absence of any deter- 

 mination of the moisture condition of the test 

 material that vitiates practically all tests of the 

 strength of timber. Since large timbers require 

 many years to season or dry in the open air, 

 while small test sticks dry out very quickly, 

 it is certain that the difference in the moisture 

 conditions will fully explain the marked differ- 

 ences which have been observed in the strength 

 of identical material in different sizes." 



Though tests for the moisture content of 

 timber are of such a simple description, that 



