Strength of Materials. 335 



407. The Constants of the Transverse Breaking Strength of 

 Wood. Since the laws given in 404, 405, and 406 apply to 

 all kinds of materials, it follows that the actual breaking 

 strength of different kinds of materials will depend upon 

 the cohesive power of the molecules as well as upon the 

 form and dimensions of the body which they constitute. 

 The breaking strength of a beam of any material is always 

 in proportion to its.breadth, multiplied by the square of its 

 depth, divided by its length, or 



Breadth X the square of the depth 

 length 



and if the breadth of a piece of white pine in inches is 4, 

 its depth in inches 10, and its length in feet 10, we shall 

 have, taking the length in feet, 



10 



Now if we find by actual trial, by gradually adding 

 weights to the center of such a beam, that it breaks at 

 18,000 pounds, including half its own weight, the ratio be- 

 tween this and forty will be 



and as this ratio is always found for white pine, when the 

 breadth and depth are taken in inches and the length in 

 feet, no matter what the dimensions of the timbers may be, 

 450 is called its breaking constant for a center load. 



For other materials this constant is different, and has 

 been determined by experiment and given in tables in 

 various works relating to such subjects. The following are 

 taken from Trautwin?. 



