300 



Mr Glazebrool', On the isochromatic curves of [Jan. 29, 



incident light, V the retardation produced by the plate at P, 7 the 

 angle between the planes of polarization and anal) T zation, and p 



the amplitude of the incident light, then if / be the intensity 

 of the light at P, 



1= p 2 \ cos 2 7 — sin 20 sin 2(0 — 7) sin 2 ^— I . 



Again, if r denote the distance CP it is easy to shew that 1" is 



r 2 

 proportional to r 2 , so that we may put F= — , a being constant. 



Thus if we put aX = c 2 we have 



/= p 2 \ cos 2 7 — sin 20 sin 2(6 — 7) sin 2 w ^[ . 



The curves of equal intensity then are given by / = constant 

 = p 2 cos 2 yS suppose, and by giving /3 all possible values from to 90° 

 we can trace the curves. 



