SOME SPECIAL PEOCESSES 



257 



side of the body-tube a mirror which has universal motion and 

 is adjustable in the direction of the length of the tube, so that 

 for low-power work with metals illumination may be carried 

 out by obliquely reflected light. The mirror is in the latter 







*A 



FIG. 70. Diagram of Path of Rays in Vertical Illuminator. 



case first adjusted approximately in position in relation to 

 the surface of the object, and then a parallel or convergent 

 beam is projected on it and reflected on to the metal surface. 

 This instrument is unfortunately not so stable in the horizontal 

 position as could be wished, but in every other respect it 



