170 PROGRESS IN MICROSCOPY 



to the objective which images A, i.e. the aperture T, at A'. Let us 

 set at A' B. reticle, symmetrical with T in relation to G. The image 

 of T and the surface fully coincide at A when the image of T being 

 reflected on S is in complete coincidence with the reticle at ^4'. There- 



sa 



Fig. 5.5. Microscope using an eyepiece with illuminated reticle. 



fore, a setting may be made on any element of the surface S. Now, 

 its normal is to be located. The reticle R is set in the focal plane of 

 the objective Oi, the reticle being in the microscope's optical axis 

 (Fig. 5.6). If the plane, tangent to the surface S at the point A, where 



Fig. 5.6. Determining the normal in a point of a small reflecting surface. 



T is imaged, is perpendicular to the microscope's optical axis, the 

 reflected beam merges with the incident beam. To ascertain that such 

 is the case, the eyepiece O2 is removed and the eye at A' is placed 



