30 



30,000 x 1,000 = 30,000,000 pounds per square inch. Or, in cross bend- 

 ing, if a bar be bent so that the stress per square inch on the extreme 

 liber directly under the load is 30,000 pounds, and the elongation of 

 this fiber in a length of 1 inch be one one-thousandth of an inch, then 

 will the modulus of elasticity be again 30,000,000 pounds per square 

 inch. For the different species of wood this factor varies from about 

 300,000 to 3,000,000. It is independent of the size and shape of the 

 piece, as also of the method of loading. 

 For uniformly loaded beam, 



5JT 5W1 3 

 ^- %±Ah~ ZlAbh 



and for beam with concentrated load in the middle, 



j, _ fl % _WP_ 

 ^- QAh~ ±Abh* 



where /is stress on the extreme fiber for the given condition of loading 

 and A is the deflection in inches, the other quantities being as before. 



The elastic resilience of a beam is the product of one-half the load 

 into the deflection at the loaded point. For a beam loaded with numer- 

 ous concentrated loads the resilience is one-half the total sum of each 

 load into the deflection of beam at that point. This quantity is a func- 

 tion of the volume of the beam. 



The elastic resilience per cubic inch, as given in Table IV, is the above 

 quantity for rectangular beams, divided by the volume. It is a measure 

 of the amount of shock that may be absorbed, without injury, by rec- 

 tangular wooden beams loaded in the middle. 



The other factors of strength are very simple and do not require 

 explanation.* 



*For the method of making the experiments, etc., see Bulletin 8, pp. 4-8. 



