'iiohen exposed to Polarized Light. 



193 



In order to understand the cause of this, we must inquire 

 into the state oC polarization of the interferinj^ pencils. The 

 ratio of refraction being the same at both surfaces of the film, 

 we have 



cos(/4-/') , ,„ ^ cos3(/ — f) 



tan <B = tan x . ■. — ^. and cot a"'= cot x . — - /. , . ,,- ; 



^ cos(/ — /') ^ cos(i + z') 



and when tan (p= cot <p"', which is the case when (p + ^"' = 90°, 

 we have 



cos^(/— i') 



tan x= T-~n\' 



cos(i + /') 



When /=90^, tan ?) = A, or the azimuth of the polarized raj', 



and cot <p = —. — , . 

 sin I 



If we now compute the values of <p and i^'" at different angles 



of incidence and in different azimuths of the polarized light, 



we shall obtain the results in the following Table. In azimuths 



0" and 90°, f and f'" = 0. 



The results in this Table, which may be considered as those of 



hence arises an irrejjiiltir system of coloured bands, with an incessant play 

 of varying tints, as if the fluid were animated. The hands of colour are 

 serrated with salient points, from wliich the fluid seems to shoot across the 

 film. Ill the oils of cinnamon, naphtha, spearmint, wormwood, rii|)eseed, 

 niitme-.'s, bcrtrainot, savine, rosemary, i^c , the phaenoiuci'.a are peculiarly 

 l)caiitifiil. With p>>p|)y oil, the red and grcenUnt^ ol'the-lth, 5th, and Gih 

 orders were also seen, 



Phil. Matr. S. 3. Vol. 32. No. 214. Mutch IS+S. O 



