100 ELEMENTARY CHEMICAL MICROSCOPY 



mits the formation of an image upon the ground glass at k' or 

 upon a photographic plate placed in position after removing k' '. 



Fig. 43 shows the apparatus functioning as a low power 

 microscope with an object illuminated by oblique rays. A 

 bracket at the back of the optical bench B carries a swinging 

 arm upon which are placed on " saddle stands," an arc lamp 

 La condensing lenses q, Q, and a ray filter y. The stage X con- 

 sists of a flat metal plate which may be leveled by the screws 

 e, e. A ioo mm. photographic lens O with iris diaphragm 

 replaces the adapter and shield used with the microscope. A 

 45 reflecting prism Y, opening downwards, is attached to the 

 front end of the photographic lens. The rays from the lamp 

 La pass through the lenses q and Q and are projected upon the 

 mirror Z attached to the swinging arm s ; thence they are reflected 

 upon the object M on the stage X. The rays from M enter Y 

 through a circular aperture, strike the reflecting prism, enter 

 the lens O, and are projected upon the ground glass k or k', 

 according as the camera mirror, described above, is or is not 

 employed. Focusing the specimen M is accomplished by Fb 

 or by focusing the camera itself or both. 



Fig. 44 shows a specimen about to be photographed by rays 

 normal to its surface. The reflecting prism Y is removed from 

 the photographic lens O. The specimen M is raised by means 

 of the extension stage table x so as to fall in the optic axis of O. 

 A plate of clear plane glass R is placed at an angle of about 45 ° 

 with the optic axis of O. Light rays from the lamp La after 

 passing through q, Q strike the surface of R and are reflected 

 upon the surface of M whence they pass through R, enter O and 

 are projected upon the photographic plate at k' . 



The instrument is normally supplied with both a Mazda lamp 

 hm and an arc lamp La, the latter operated by clock work. The 

 type of Mazda lamp selected by the maufacturer serves fairly 

 well for visual examinations but in the opinion of the author 

 is not suited to photography. 



The plate holders are for metric size plates. 



The most noteworthy improvements in this instrument are 

 in the mountings of the vertical illuminators and in the con- 



