66 



TIMBER AND TIMBER TREES. [CHAP.X. 



Fir of the same dimensions, as shown in subsequent 

 Tables, might be loaded to 67 tons. 



As before stated, I have applied this description of 

 test to a great variety of woods, and it has enabled me 

 to ascertain with tolerable accuracy the amount of strain 

 they will each bear to the square inch, of base. The 

 general result of the trials with gradation of lengths 

 confirms, in some degree, the theory of a four-fifths pro- 

 portion of base to length, and shows it to be at least 

 approximately correct. Therefore, with this data for 

 our guidance, aided by a little practical judgment, there 

 should be no difficulty in determining the scantlings of 

 props and supports for all ordinary purposes. 



There is yet another description of test to be noticed, 

 namely, that for ascertaining the elongation of the fibres 

 under certain strains. The experiment was made in one 

 of the royal dockyards upon two pieces of English 

 Oak, each 2 x 2 x 48 inches, and very carefully con- 

 ducted note being taken of the elongation in a length 

 of 3 feet ; the mean results were found to be as follows, 

 viz. : 



TABLE XXIII. 



