8 INTRODUCTION. 



from larger ones * The botanical accuracy of a specimen is 

 not always certain, therefore figures relating to the physical 

 "operties of wood should be employed with greater caution 

 than those relating to the more homogeneous metals. 



Many of the experiments conducted to establish statements 

 regarding the physical properties of wood have been defective 

 in that while the conclusions were correct as applied to the 

 specimens immediately studied, such specimens did not stand 

 for the species at large. The recognition of difficulties t 

 selection of specimens, the scientific standardizing of 

 so that results could be generally utilized, as distinct from the 

 simple manipulation of specimens in testing-machines, have not 

 been exhaustively attempted until recently.! 



The tests that have been made to obtain measures for woods 

 may be arranged in several groups, each one depending upon the 

 way in which test pieces were selected. The groups are as 



follows : 



(i) Professors Fernow and Johnson acknowledged the diffi- 

 culties that have been noted in a series of experiments conducted 

 for the United States Division of Forestry. The details con- 

 sidered and the methods evolved during this study were of such 

 nature as to influence all subsequent efforts. These figures are 

 believed by many to be the most satisfactory in existence. The 

 study is disappointing in that results were obtained for so few 

 species. Some of these are of secondary importance com- 

 mercially. 



(2) Experiments were conducted for the Tenth United 

 States Census by Mr. J. P. Sharpless at the Watcrtown 

 Massachusetts Arsenal. It is certain that the specimens were 

 of the exact species credited; but in other ways selections were 

 not guided by factors that would now be considered. The 



* Only because imperfections are moie likely in larger pieces. Large and 

 small pieces of equally perfect wood are equally strong. (Also see Publications 

 U. S. Forestry Div.and J. B. Johnson's " Materials of Construction," p. 462.) 



t It should be noted that the selection and preparation of specimens require 

 the exercise of more judgment than the simple testing of speimens, if the con- 

 clusions are to be such that they can be generalized from. 



