Bauhaus-Universität Weimar

Titel:
Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Person:
Gage, Henry Simon and Henry Phelps Gage
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39438/655/
Ch. XV] 
DARK GROUND ILLUMINATION 
647 
will appear changed as in the case of projection. The sharpness of 
the pattern, and the intricacy of design are however much finer 
than it is possible to project. 
Fig. 374. Demonstration of the Abbe Diffraction Theory to a Single 
Observer. 
L Arc. 
C, Condenser. 
S Pinhole or Slit. 
C2 Condenser, preferably an achromatic combination. 
G Grating. 
T Telescope with high power eyepiece. 
The telescope is focused on the grating and the diffraction pattern is focused 
just in front of the telescope objective. By placing suitably shaped dia¬ 
phragms at this point, the image as seen in the eyepiece will be modified. 
Dark Ground Illumination : Method of Striae 
§ 912. Many beautiful experiments in Physics and Chemistry 
can be shown by what is best known as the Schliren-methode of 
Toepler. This method will yield results almost as striking as those 
obtained by polarized light. 
See Wiedemann Annallen, CXXXI, p. 33. 
The use of this method enables one to demonstrate any slight 
lack in homogeneity of a medium which is sufficient to deviate a 
beam of light. 
To adapt this method to projection the following apparatus can 
be used: 
§ 913. Apparatus for the experiments with striae.— 
(1) Magic lantern with the usual equipment of arc lamp, 
projection objective, and the first element of the large condenser. 
(2) A special condensing lens or combination. This need not 
be of especially large diameter or short focus (5 cm. diameter, 20 
cm. focus will answer), but it should be as free as possible from 
spherical and chromatic aberration, and must have no scratches 
and be kept perfectly clean.
        

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