262 



PKACTICAL PHOTO-MICROGRAPHY 



that the illuminator may be used in any direction that is, in 

 front or at either side. By sliding it up and down in a dovetail- 

 fitting the illuminator can be placed at any given distance from 

 the back lens of the objective, and may also be moved at right 



FIG. 73. Engineers' Metallurgical Microscope. (J. Swift & Son.) 



angles to the optic axis. An iris- diaphragm is also fitted for 

 use in conjunction with the vertical illuminator, and this 

 constitutes a most valuable accessory in actual work, as it is 

 often necessary to be able to reduce the angle of the illuminating 

 beam, 



