63 
No. 
B. Illuminating Apparatus 
for speetroseopieally decomposed light. 
21 
When it is required to illuminate a portion of an object in 
the field of the microscope with a single pure spectral colour or 
to observe the effect of the whole spectrum upon it, or finally 
to study the effects of the spectrum of polarised light, the instru- 
ments Nos. 21, 22 or 23 have to be used. These are connected 
to the Abbe illuminator by the centering collar supplied with 
each instrument (vid. Fig. 23, p. 64) and adjusted to the object 
plane by the rack and pinion motion of the illuminator. All three 
instruments necessitate, unless used with either stand I 
or I**, an inclined position of the stand. 
Fig. 22. 
Illuminating: apparatus for monochromatic lig^lit. 
Illuminating Apparatus for monochromatic light after 
HARTNACK. The light which emerges from the slit Sji is rendered 
parallel by means of the collimator lens C, is then spectrally 
decomposed and projected upon the specimen by means of the 
projection objective 0. The spectrum is sufficiently extended to 
ensure approximately uniform monochromatic illumination with 
higher powers. By adjusting the position of the slit by means of 
Marks 
