242 



BLACK APPARATUS FOR MICRO-PROJECTION [Cn. IX 



eter into the center of which is screwed the objective (fig. 138), then 

 the field is not at all restricted. The low power objectives can be 

 focused easily by moving their supports back and forth along the 

 optical bench by hand (fig. 158-159). 



FIG. 136. MECHANICAL STAGE OF WIDE RANGE. 



(Cut loaned by the Bausch c? Lomb Optical Co.). 



This mechanical stage can be attached to any microscope with square stage, 

 and it permits the use of large slides. The right to left scale is 80 mm. and the 

 front to back one 58 mm. The actual range available depends on the size of 

 the stage of the microscope. 



BLACKENED APPARATUS 



370. The light necessary for micro-projection is so dazzling 

 that it should IDC kept strictly within the projection apparatus by 

 means of a proper lamp-house and bellows, so that the only light 

 which finally reaches the screen is that which passes through the 

 projection objective. But this ideal condition cannot be wholly 

 realized in practice, hence the necessity of making the outside of 

 the entire apparatus, from lamp-house to microscope tube, dull 

 black. Then any escaping light will not be reflected from polished 

 surfaces and scatter light into the room, on the one hand, or blind 

 the eyes of the operator and annoy the auditors on the other. 

 Projection apparatus found in institutions, in many cases, have a 

 finish of polished brass or nickel. If the operator cannot focus 



