TABLE 78. 



ELASTIC MODULI. 



Rigidity Modulus.* 



* The modulus of rigidity as used in this table may be shortly defined by the following equation : 



Modulus of rigidity - Intensity of tangential stress. 

 Distortion in radians. 



To interpret the equation imagine a cube of the material, to four consecutive faces of which a tangential stress of 

 uniform intensity is applied, the direction of the stress being opposite on adjacent faces. The modulus of rigidity is 

 the number obtained by dividing the numerical value of the tangential stress per unit of area by the number repre- 

 senting the change of the angles on the nonstressed faces of the cube measured in radians, 

 t Lord Kelvin. 



SMITHSONIAN TABLES. 



74 



