NUMBERS AND MEASURES. 



17 



deformation which it produces. The deformation is measured by 

 the change (in radians) produced in any one of the four angles of the 

 square bar. 



Glass (mean) 150 



Glass (flint) 243 



Brass (mean) 350 



Brass (drawn) 373 



Copper 456 



Iron (cast) 542 



Iron (wrought) 785 



Steel 834 



(21) ELASTICITY AND TENACITY OF SOLIDS. 



"Young's modulus of elasticity" (Y) is the amount of end-pull 

 or end-thrust required to produce any very small elongation or con- 

 traction of a bar multiplied by the ratio of its length to the 

 elongation or contraction produced. 



The tenacity (T) of a substance (density A) is the greatest longi- 

 tudinal stress which it can bear without tearing asunder. 



The quotient of the tenacity by Young's modulus gives the 

 greatest longitudinal elastic extension that the substance can bear. 



The stresses are given in tonnes (1 000 000 grams) per square 

 centimetre. 



