Measurement of Young's Modulus. 



403 



In the statical method a small weight is hung on the 

 needle at a measured distance from the centre. This produces 



Fig. 1. 



a known difference between the tensions in the wires, and the 

 consequent difference in extension can be measured on a 

 scale by a beam o£ light reflected from a small mirror 

 attached to the needle. By hanging the mall weight at 

 various distances a series o£ measurements can be made. 



I. First Oscillation Method. 



IJie Seedle. — The vibrating needle AB may be conveniently 

 made of a straight bar or tube with a heavy cylinder fixed at 

 each end of the bar by set screws. If these cylinders are 

 hollow, and each made with four set screws placed as shown 



