VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 83 



The prism P and the disk k are attached respectively to the axis 

 of the milled wheels W and W. These in turn are mounted upon 

 metal plates with edges obliquely cut so as to fit into the dove- 

 tail d. These plates when inserted and pressed in place are held 

 by the spring s. They are thus se- 

 cured in proper position but can be 

 slid back and forth in the slot d. 

 A mark S upon the plates and an- 

 other / upon the adapter serve to 

 indicate the proper position of P or 

 k with respect to the optic axis of 

 the microscope M. To remove the 

 prism, the wheel W is pressed gently 

 downwards and outwards, thus re- 

 leasing the plate from the spring s; 

 W is then carefully raised until the 

 plate is free from the slot d. It 

 can then be removed by tipping up 

 slightly and withdrawing from the 

 opening. To insert the disk, turn W 

 until the groove i is horizontal, introduce k into the opening and 

 push down till the lower edge fits into d, then press W forward 

 as far as it will go. The groove S is then brought into coincidence 

 with /. The reflecting disk k is fastened to a mounting by the 

 spring fingers v. This device permits the rapid and easy removal 

 of the disk for cleaning or for replacement when broken. The 

 objective O is screwed into the lower opening of K; in the illus- 

 tration is an 8 millimeter apochromatic, for 200 millimeters tube 

 length, uncorrected for cover glasses. 



Just as in the simple prism or disk illuminators, the rays of 

 light striking the reflecting surface are directed downwards 

 through the objective upon the object m. 



Parallel light should fall upon the lens L. This is obtained by 

 employing a suitable lens between the illuminator and radiant. 

 The Leitz Company supply a very conveniently mounted lens 

 for this purpose. A metal screen A, Fig. 38, is attached to a 

 stand B. Mounted in the screen is a lens in front of which is an 



FIG. 37. Leitz Vertical 

 Illuminator. 



