416 PROFESSOR STOKES, ON THE COMPOSITION AND RESOLUTION, ETC. 



independent of the former, of the same intensity, polarized at an azimuth zero. This result 

 may be compared with one of Professor Dove's experiments. 



If a rotating crystalline plate, cut from a doubly refracting crystal in a direction not 

 nearly coinciding with the optic axis or one of the optic axes, and not sufficiently thin to 

 exhibit colours in polarized light, be substituted for the rotating Nicol's prism, since the 

 plate is too thick to allow of the exhibition of any phenomena depending on the interference 

 of the oppositely polarized pencils, the effect will be just the same as in the case of the 

 Nicol's prism, only the intensity of each steam will be doubled. 



In applying the formulae of this paper to experiments in which one part of an optical train 

 is made to revolve rapidly, it must be understood that the other parts of the train are at rest, 

 or at least do not revolve with a velocity nearly equal to the former. Otherwise, particular 

 phenomena will be exhibited depending on the simultaneous movements of two or more parts 

 of the train, as appeared in Professor Dove's experiments; and in the calculation of these 

 phenomena it will not be allowable to substitute for the stream of light emerging from the 

 polarizer, or first revolving piece whatever it be, the streams of common and elliptically 

 polarized light to which, for general purposes, it is equivalent. 



G. G. STOKES. 



