The Out fit -Rods. 



35 



stiffness and elasticity are but other terras to express the 

 resistance offered by the material of the rod to this en- 

 forced change. 



Now suppose we take two pieces of wood each of one 

 square inch in cross-section, and, laying one upon the 

 other, lash them together as firmly as we can in the posi- 

 tion shown at A in the cut. 



This I will hereafter call the "compound stick." 



Fig. 2. 



Let us also prepare a single piece of wood JS like the 

 other in every respect, except that its cross-section meas- 

 ures one inch by two. It is therefore of exactly the same 

 dimensions as the compound stick we have made by lash- 

 ing the two inch-square pieces together. 



Now let us place the ends of the single and of the com- 

 pound stick upon equidistant supports so that both rest 

 on edge, and impose an equal load on the middle of each. 

 Each stick will then oppose to its load a section of 

 material one inch wide and two inches in perpendicular 

 depth, in short, an exactly equal length and quantity of 

 material, disposed in exactly the same position, to meet 

 an exactly equal strain. 



