180 PROGRESS IN MICROSCOPY 



Since <5^;./2 and e = 20/^, then, n'-fi^OOl and 



/](«'— /;)- 0001. 



In the example selected, the absolute error J« is approximately one 

 unit to three places of decimals. 



Accuracy can be greater but, as will be seen later (Chapter VIII, § 2), 

 a prominent factor, the incident light N.A., takes effect in measure- 

 ment accuracy. 



