24 INTRODUCTION. 



of elasticity from 25699 (in Ficus aurea, the Small-fruited Fig,) to 

 165810 (in Larix occidentals, the Western Tamarack). 



119. The Modulus of Rupture, as denned by Prof. Thurston,* is 

 " the quantity which represents the stress upon a unit of area of cross- 

 section of the fiber farthest from the neutral axis [i. e., the line of par- 

 ticles not subjected to either tensile or compressive stress] on the side 

 which gives way, and at the instant of breaking under transverse stress/' 

 This is expressed in the results of Mr. Sharpies' experiments in kilo- 

 grams, the unit of area of cross-section being a square centimeter. In 

 the three hundred and ten species experimented upon, he found the 

 range to be from 148 (in Bursera gummifera, the Gumbo Limbo,) to 

 1394 (in Carya myristicaeformis, the Nutmeg Hickory). 



120. Resistance to Longitudinal Pressure is represented by the 

 number of kilograms required to crush the fibers of a stick one centi- 

 meter square by longitudinal pressure. It is the ultimate weight which 

 a stick of that size will support, and in the three hundred and seventeen 

 species experimented upon, the range of variation was found to be from 

 155 (in Bursera gummifera, the Gumbo Limbo,) to 887 (in Eugenia buxi- 

 folia, the Spanish Stopper). 



121. Resistance to Indentation is expressed in the number of 

 kilograms required to sink a punch one centimeter square to the depth 

 of 1.27 millimeters perpendicularly to the fibers of the wood, i. e., into 

 the side of the grain. Three hundred and fourteen species were tested., 

 and in them the range of variation was found to be from 47 (in Bursera 

 gummifera, the Gumbo Limbo,) to 793 (in Guaiacum sanctum, the Lig- 

 numvitae). 



122. The word " compact" as applied to timbers by Prof. Sargent in the 

 report above referred to, designates a non-liability to check in seasoning. 

 It is mainly upon the authority of that report that the term is used in 

 this work. 



* The Materials of Engineering. By Robert H. Thurston. Part I, p. 94. 



