MEASURING REFRACTION INDICES— POLARIZING MICROSCOPES 185 



Newton's colour scale 



tint b m a:.. The measurements b and c evince {n'-n)e by means 

 of equation (7.4). As stated previously, the arrangement achieved is 

 not necessarily the one shown in Fig. 7.3. Figures 7.4, 7.5, 7.6 and 7.7 

 show the other contingent arrangements. There is no chance for 

 errors as, when determining a and b, \{ b > tf. Fig. 7.4 must be con- 

 sidered when n > n and Fig. 7.5 when n > n . When b < a, the 

 figure obtaining is Fig. 7.6 when // > //', and Fig. 7.7 when n > n. 



