POLARIZED LIGHT: 



109 



35 25". This tube may be made of cardboard, as 

 shown in Fig. 30 (also the exact dimensions). The 



Fig. 29. 



width from a to b, and c to d =12 mm., that from 

 b to c, and d to e, equal to the length of the thin 

 glass, when placed at the proper angle. It will be 

 found convenient to cut the cardboard partially 



9 

 Fig. 30. 



through with a sharp knife from b to/, c to g, and 

 d to h ; near the bottom of the first division on 

 the other side paste a strip of card i ; carefully 

 paste the two edges of the card together; drop 



