CAMERA LUCIDA. 
57 
Fig. 25 sliow8 this camera, mounted in rig. 25 . 
a cap, which fits the top of the eye-piece. 
If the microscope is inclined at an angle 
of thirty degrees with the horizon, this 
camera may be used in the Same manner 
as Wollaston^ s Camera Lucida^ described 
in the previous section. 
With this camera the microscope is 
sometimes placed in a . perpendicular posittion, and the drawing 
made on a table which is inclined. 
76. Soemmeriiig’§ Steel Speculum. This 
is a plane speculum of polished steel, smaller 
than the ordinary pupil of the eye, commonly 
set at an angle of 45°, and mounted as shown 
in Fig. 26, and attached to the eye-piece in the 
same manner as the camera. 
This speculum is so mounted that its angle of inclination 
may be changed to project the image on any part of the paper 
where it is most convenient. With this instrument, the 
reflected image of the object, and the pencil, both appear 
together on the paper, and the microscope may be placed at 
any angle which is found most convenient. 
77. Using the Camera. In using the camera lucida, or 
speculum, some care is required to see both the object and the 
pencil at the same time. Sometimes the light on the paper is 
to6 strong, and it requires to be shaded by a book or other 
object. In the evening, on the other hand, the pencil and 
paper require additional illumination. If the object and pencil 
are not both visible on the paper at the same time, the diffi- 
culty will generally be overcome by moving the eye about till 
the proper position is found, and -when once obtained the eye 
should be kept steadily in that position till the drawing is com- 
pleted. 
To have different drawings on a uniform scale, it is neces- 
sary to have the microscope always inclined at the same angle, 
that is, to have the camera at a uniform distance above the 
paper. Nine inches will generally be found the proper dis- 
Fig. 26 . 
CATALOGUE OF ACHROMATIC MICROSCOPES. 
