it an 
circular Polarization of Light in Liquids. 245 
screw (g). ‘Fhe part carrying the tubes 
(¢¢) consists of a frame holding them in 
a vertical position, each tube being in- 
closed in an opake case. The whole 
frame with the’ tubes is made to turn 
about the pivots (bd), so that either tube 
in succession can be brought over the 
hole (q), and with its axis in the line of 
the ray. Fig. 4 is a section of one of the 
tubes in its opake covering, to show the 
manner of its fitting into the frame at the 
bottom, in which the opening is cut so as 
just to allow the tube to rest against its 
edges, and to leave an opening as large 
as the area of the polarizer. 
