The Outfit— Rods. 



35 



stiffness and elasticity are but other terms 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 3 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. 



