6o 



Image-erecting Microscopes, 



provided with PORRO Prisms. 



In the course of 1897 we introduced a new form of binocular microscope 

 in which stereoscopic vision is obtained, not by division of a pencil of light 

 passing through a single objective but by a combination of two microscopes, 

 complete in themselves and provided with erecting prisms. 



In the Stands X a , X b and X the double tube is adjustable by means of 

 rack and pinion. 



The application of erecting oculars fitted with PORRO Prisms 

 affords a convenient means of adjustment for varying inter-pupillary distances. 

 The paired objectives are mounted upon slides and require adjusting for 

 each stand separately. Consequently it is necessary to send us the 

 tube when subsequently ordering paired objectives. 



The mount of one of the objectives is provided with screw threads to facilitate equally sharp 

 focussing of both lenses in cases where inequalities of power of vision in the two eyes require com- 

 pensating. 



We supply paired objectives for these microscopes in five series (see p. 23), 



viz: (55), (ao), (a?), (a?) and (pT). 



The magnifications obtainable by combinations of the above objectives and 

 oculars range between 8 and 72 diameters; see tables on p. 26, which also 

 contain data of free working distances and of diameters of the visible areas of 

 objects. 



It should be observed, that the objective (pf) can only be used as a water immersion 

 system. (See p. 21.) 



The movement of the casings of the PORRO Prisms is sufficient to admit 

 of adjustment for any inter-pupillary distance within normal limits (56 76 mm 

 = 2l /4 3 to-)- In cases where the eyes are abnormally far apart or close together 

 the actual measurements should be specified when ordering. 



