SCIOPTICON MANUAL. 



199 



or other object, in the aperture at 0; after which it is 

 brought to a focus by the object-glasses at jP, and finally 

 again polarized, or analyzed, by the Nicol's prism P, and 

 thence thrown on the screen, the disc on which should 

 not exceed three feet in diameter. 



Fig. 57. 



The phenomena connected with the polarization of 

 light are attended by a most gorgeous display of colors, 

 and are, in consequence, among the most attractive in 

 the whole range of physical optics ; an apparatus, there- 

 fore, which facilitates their exhibition to an audience 

 becomes a most valuable adjunct to the magic lantern. 



The subject itself is, however, of too recondite a nature 

 to admit of adequate treatment in the present manual; 

 the reader is therefore referred to Pereira's lectures on 

 " Polarized Light/' " Ganot's Physics," and other works 

 on Physical Optics. 



The objects best suited for the polariscope are designed 

 with films of selenite of various thicknesses and forms; 



