Optical Determination of Stress. 



751 



where p is the mean radius of curvature, c is the distance of 

 the applied force from the centre of the section, and y u y 2 

 are constants depending on p , 77, and T. In the present case 

 ry 1= 1*048, 72 = '891, where 77 = *39, and the position of the 

 neutral axis is "055 in. from the centre on the tension side. 



Fi-. 7. 



.o-& 1 



This agrees fairly well with the observed value of *059 in. 

 having regard to the fact that p is increased about 10 per 

 cent, of its original value by the load. 



Owing to the uncertainty of the exact position of the 

 forces when a ring of such great curvature is stressed and 

 somewhat distorted by a load, it has not been possible with 

 the apparatus at my present disposal to establish any very 

 accurate relationship ' between the external and internal 

 forces. 



The present examples, however, serve to illustrate the 

 practical uses which it is possible to make of this method of 

 analysing the stresses produced in any object capable of 

 being represented in a plane by a model cut from a sheet of 

 transparent material. 



