﻿in a Rectangular Bar by means of Polarized Light. 9 

 in the notation of § 3, S = 0, or 



p= S'' s=o ' Q=o - 



(8) 



For the purpose of this verification the isochromatic lines 

 were used, as well as the isoclinic. For an isochromatic line, 

 if S = 0, Q = 0, P should be constant. Hence, if equations (8) 

 are correct, the isochromatic lines should be parallel to the 

 horizontal edges of the bar. The isoclinic lines should reduce 

 to a single dark band along the axis of the bar (y = 0), 

 except when i=0 or 90°, when the whole field should be 

 dark. 



The span of the beam between the supporting knife-edges 

 being 30 cm. a sufficient couple was applied to make visible 

 the coloured band of the first order, both above and below 

 the neutral axis. The line where the red passes into the blue 

 was very sharply defined and easily measured. 



Measures were taken at the mid-section and at various 

 distances from it. The results are given below. 



Table II. 



Distance 



from 



mid-section. 



Distance of upper 



Isochromatic 

 from upper edge. 



Distance of 



black band 



from upper edge. 



Distance of lower 



Isocbromatic 

 from upper edge. 



- 14 cm. 



•45 cm. 



1-80 cm. 



3-10 cm. 



-10 „ 



•45 „ 



1-80 „ 



3-10 ,, 



. - 5 » 



•50 „ 



1-82 „ 



3-10 „ 



„ 



•50 „ 



1'82 „ 



3-10 „ 



+ 5 „ 



•47 „ 



1"78 „ 



3-10 „ 



+ 10 „ 



•45 „ 



1-77 „ 



3-10 „ 



+ 14 „ 



•45 „ 



1-77 „ 



310 „ 



In the above the two isochromatics are equally distant 

 from the black band, and all three are horizontal, the diver- 

 gences being within the error of observation. This shows 

 that the stress difference is constant as we move parallel to 

 the axis of the beam, and that the tension and pressure above 

 and below are numerically equal at equal distances from the 

 neutral axis. 



The above observations were taken with the nicols inclined 

 at 15° to the vertical. On rotating them the black band 



