PLATE III 



200ro/i 



300 m/i 



400 m/^ 



500 m^ 



600 m// 



700 m/t 



NICOLS NICOLS 



CROSSED PARALLEL 



(a) (b) 



Fig. 1. The first order in Newton's colour series as shown 



by a quartz wedge (a) between crossed Nicols; (6) between 



parallel Nicols. 



Fig. 2. The appearance of starch grains between crossed Nicols over a plate, 

 Red 1. For explanation, see text, p. 64. 



\Betwei'n pp. 64/65 



