Uses of the Projection Lanterns. 159 



tical bench as far away from the condenser as possible. If the last-named slit be gradually narrowed 

 the coloured diffraction bands will result. 



Polarisation. The phenomena attending the polarisation of light can be shown with the Po- 

 larisation Apparatus Xo. 51,074, this apparatus being specially adapted for the purpose. A fuller de- 

 scription is contained on p. 1212 (see end of present Section). 



Double Refraction. The two spectra appearing simultaneously are projected with the aid of 

 a calc-spar prism (the refracting edge of which is parallel to the principal crystallographic axis) in 

 exactly the same manner as described for a spectrum in the spectrum phenomena. The Polarisation Ap- 

 paratus (Xo. 51.074) previously mentioned is also suitable for carrying out further experiments with 

 rapidly annealed gL Jr-spar lamellae, preparations of gypsum and mica, etc., as this apparatus 



: up ready for use in front of the lantern as the preparations have only to be inserted and rotated 

 in their plane. 



Microscopical Preparations. 



The projection microscope No. 51,047 is screwed into the objective holder (or Xo. 51,048 is 

 inserted on the slider of the optical bench) and it is introduced into the path of the converging rays 

 issuing from the condenser in such manner that their point of union strikes the microscopical preparation. 

 A water trough Xo. 50,976 or 50.977 is used for preventing the preparation from becoming heated. 



The microscopical preparations are fixed under the spring clamps of the object stage. The 

 sharpness and brilliancy of the images are then secured by turning the knob. For finer focussing, which 

 is necessary at very great magnification, a special screw knob with micrometer screw, to be found in 

 the case of the Projection Microscope No. 51,048 underneath the object stage, is provided. The ap- 

 paratus is arranged for projecting without an ocular, as in most rases a moderate degree of magni- 

 fication, say 500 times, is sufficient. One of the objectives Xos. 51.049 51,053 is required in addition 

 to the microscope, those used being chiefly the ones numbered 2, 3 and 5. If a number of objectives 

 are available, it is advisable to use a revolving nose piece (Xos. 51.054 or 51,055) for changing the ob- 

 jectives, so as to render it possible to pass from one magnification to another with expedition. 



Opaque Objects. 



For presenting and magnifying illustrations, especially wood cuts from text books, one of the 

 Megascopes Xos. 51.045 or 51.046 is used. When using this either the whole or a part of the condenser 

 should be removed in accordance with the instructions in the price list. 



The Projection Lantern as a Source of Heat. 



In addition to being employed as a source of light the projection lantern can in a number of 

 - In- specially used as a source of radiant heat, e. g.. for absorption experiments with coloured 

 glasses. 



Miscellaneous Applications. 



It may be well to mention here that the experiments just described do not by any means ex- 

 haust the experiments which it is possible to carry out with the projection lantern. There are still a 

 number of experiments, especially relating to light, which may be carried out by the aid of the pro- 

 jection lantern; but these are not given here, since the Projection Lanterns are only used as the source 

 of light for these and special provision for the same does not need to made in the lantern. As regards 

 the conduct of these experiments, therefore, reference must be made to the literature mentioned in the 

 list and to the instructions for use which we append to the apparatus when supplying. 



Mention may, however, be made of the use of the lantern for photographic enlargements, 

 for copying with high-speed sensitised papers: also for the projection of cinematographic pictures, 

 projection of pictures in their natural tints by subtractive colour reproduction with the Projection 

 Chromoscope as suggested by Ives, or by additive reproduction with the Diffraction Chro- 

 moscope. 



Further fields for the utilisation of projectors are given in the work of Drs. Hassack and Rosen- 

 berg entitled ..Die Projektionsapparate". Vienna and Leipzig. 1907. A. Pichlers Witwe & Sohn. All 

 the apparatus mentioned in this work are supplied by us. and many other pieces of apparatus in ad- 

 dition in accordance with the best known and most used text books are included in our price list. 



