148 . Transactions of the Society. 



light or lamp-light may be directed directly upon the polarizer, 

 but in the case of a vertical microscope a piece of plane mirror 

 should be laid upon the table in front of the microscope to receive 

 the light and direct it upward to the polarizer (see sketch). 



If the light given by a single blackened plate is insufficient, it 

 may be increased by superposing a second 3x1 slip upon the 

 blackened plate. 



The curve given by Stokes (see p. 147) will be of interest to 

 microscopists. 



From this curve it will be seen that practically the maximum 

 amount of polarized light which can be obtained by reflection is 

 obtained with eight plates. In practice one, or at most two, are 

 sufficient for subjective work. 



The simple vertical microscope can be adapted very simply for 

 observation in polarized light by cementing a slip-polarizer to a 

 small block of wood adapted to slide between the sides of the 

 horseshoe foot. 



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UEVJS 



Cyi-flS-i 



Analyser. — This must be some form of Nicol, and it should be 

 mounted to rotate. Perhaps the most generally useful form is a 

 small and therefore square-ended Hartmack prism in a separate 

 mounting, which can be placed when desired above the eye-piece. 

 The Abbe polarizing eye-piece is convenient for many purposes, 

 but it is not well known. It consists of a double-image prism 

 mounted between the eye-lens and the stop of a Huygenian eye- 

 piece. The prism and eye-piece combined project two images of 

 the aperture of the object-glass into the plane of the Eamsden 

 circle, one centrically and the other eccentrically. The eccentric 

 image is stopped out, and the light passing through the centric 

 image only is allowed to enter the eye. This analyser should be 

 used with an ordinary eye-piece of aljout the same power, adjusted 

 so that one eye-piece can be substituted for the other for refocusing. 



