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 
L(Z 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 loo 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 z; 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 0, 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 H2 
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 0 . 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 
Lw 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- 
