﻿in a Rectangular Bar by means of Polarized Light. 3 



Maxwell himself, in the paper referred to, indicated the 

 value of these lines for the purpose of experimentally deter- 

 mining the stress system inside an elastic solid, and gave 

 several examples. Later, Professor Carus Wilson (Phil. 

 Mag. ser. 5, Dec. 1891) applied the method to the investi- 

 gation of the stresses in a beam bent by a central load, but 

 restricted himself almost exclusively to the study of the 

 stresses in the mid-section of the beam. He has, however, 

 given a drawing of the isoclinic lines and deduced from them 

 by Maxwell's method the lines of principal stress, but has 

 not discussed them further. 



Quite recently Professor E. G. Coker, in a paper on the 

 distribution of stress in plates of variable section, read before 

 the Institution of Naval Architects, April 7, 1911, has applied 

 the method to the study of problems connected with the 

 effects of rivet holes; he has made use exclusively of the 

 isochromatic lines. 



The experiments of which the present paper gives an 

 account were carried out in the Engineering Laboratory, 

 Cambridge, in 1901, with the object of extending the results 

 of Carus Wilson. Owing to various circumstances and 

 pressure of other work, they have remained hitherto un- 

 published. Nevertheless the author believes that the same 

 ground has not been covered since. 



§ 2. Description of Apparatus. 

 Plate I. shows a photograph of the actual apparatus used, 

 of which figs. 1 and 2 give a diagrammatic representation in 

 plan and elevation. 



Fkr. 1. 



The 



knife-edge 



ass bar AB, of rectangular section, rested on two 

 3 C, D, supported by two wooden blocks E, F, 

 B 2 



