GEOMETRICAL MEASUREMENTS 



169 



made through the front plane along A... The two transverse settings 

 yield the length A^B^ and the two axial ones the distance e. The actual 

 line v^i^i then equates | (A.yBi-r^-). If the length /^i ^2 is encompassed 



Fig. 5.4. Measuring a length by means of lateral and axial settings. 



in a medium of index n, e is to be multiplied by n. In such a measure- 

 ment, the microscope optical axis is not to be shifted and, in a series 

 of measurements, the dispersion in performance data provides the 

 limits of accuracy. 



6. MEASURING SMALL AREAS AND VOLUMES 



Compounding the measurements described in § 3.4 and 5 evinces 

 the data required. Surfaces may also be measured by means of an 

 integrating stage or an integrating eyepiece. This is tantamount to 

 cutting up the object in surface elements and simply adding them 

 up by means of the integrating stage. 



7. DETERMINING THE NORMAL IN A POINT OF A SMALL REFLECTING 



SURFACE 



The standard microscope eyepiece is to be substituted for one of 

 special design (Fig. 5.5). The aperture of screen E is illuminated by 

 the lamp L. The light, originated from T is reflected by the 45^-slanted 

 semi-reflective mirror G. The microscope is adjusted so as to image T 

 in the investigated surface S. A is imaged in the area whose orien- 

 tation is sought. After being reflected back from the surface S on 



