52 



a. The size of the specimen can vary from a small crystalline 

 grain to very large structures. 



b. The tests can be telemetered. 



c. Measurements can be automated by means of photocells 

 and servo-mechanisms. 



d. An analysis can be made in almost any atmospheric condition. 



p. An analysis can be made with the specimen connpletely sub- 



mersed in any transparent liquid such as water or oil. 



f. With normal incidence readings, the strain (or stress) 



is obtained at a point rather than over a finite gage length. 



g. The individual principal stresses at a point can be obtained Avith 

 great accuracy from nornnal and oblique incidence readings if 

 the specimen, is symmetrical. 



h. If a specimen is not symmetrical, the integrating effect due 



to gage length can be varied when the individual principal 

 stresses are to be obtained. 



i. The strains (or stresses) can be obtained exactly at the edge 



of free boundaries'^^* ^°'. 



