INTRODUCTION. 9 



series is valuable because it includes almost all American species 

 and the results are the ones that are quoted in several text 

 books. 



(3) Some experimenters believe that practical figures may 

 be obtained by testing large or life-sized pieces such as are 

 actually used in construction. Professor Lanza is an advocate 

 of this basis, which has also influenced experiments more 

 recently inaugurated by the National Forest Service under 

 Professor William Kendrick Hatt. 



(4) The later series of investigations inaugurated by the 

 National Forest Service and to which allusion was made in the 

 preceding article is characterized by the fact that much attention 

 is also paid to mechanical properties other than strength. This 

 study includes investigations of physical properties such as 

 shrinkage, and it also includes technological processes such as 

 kiln drying, the application of preservatives, and the application 

 of fire retardants; some of these matters are considered as they 

 influence strength. This investigation is in charge of Professor 

 William Kendrick Hatt. 



(5) All other experiments are in this group. Many experi- 

 ments have been made from time to time which are not 

 characterized by any particular method or principal such as 

 separate the investigations that are noted in the preceding 

 articles. Details as to selection are incompletely given or are 

 absolutely lacking, and the results differ very widely from one 

 another. Such studies are referred to as are noted in the works 

 of Hatfield, Lazlett, Rankine, Thurston, and many others. So 

 far as is known some of these experimenters simply " broke 

 specimens." Some series within this group are valuable in that 

 they enable comparisons. Professor Rankine and Mr. Lazlett 

 experimented principally upon foreign woods. 



The figures established by the United States Bureau of 

 Forestry and alluded to in item i, page i, appear, so far as 

 they exist, upon the following pages. Where they do not 

 exist, the leading spaces set apart for them are left vacant for 

 other insertions as preferred. 



The coefficients appearing in this book are, then, 



