262 



PROJECTION MICROSCOPE 



[CH.IXa 



distance not exceeding 5 meters ; 3 meters would be even more satis- 

 factory. For size of field and magnification see the table 425. 



416. Arrangement of the Parts of the Projection Micro- 

 scope. As stated in section 399, all the parts of the apparatus should 

 be separately adjustable. This is because the arrangement needs to be 

 somewhat different for different objectives. 



FIG. 209 



FIG. 209. To show the elements of the illuminating and condensing apparatus 

 used in Fig. 204, and the position in the cone of light of objects of various sizes- 

 This figure shows the necessity of moving the stage to accommodate objects of 

 various sizes and ensure their complete illumination by the entire cone of light from 

 the condenser. 



i. Focus of the condenser where objects for high powers are placed. 2, j. Posi- 

 tion of larger objects. 4. Front ten's of the condenser. 5. Laige water bath. 

 6, 7. Two lenses of the condenser next the radiant. 8. The dotted line over the 

 meniscus represents the sheet of mica which serves to prevent the too rapid heating 

 of the lenses. This is very satisfactorily held in position by a cap of sheet iron or 

 copper. ( It is in position in 204 and 205 D. ) 



The guiding principle is that the specimen should be lighted by a 

 converging cone of light, and it should be lighted by the entire cone of 

 light traversing the lamp condenser. If one uses a white card it is 

 easy to determine the position and size of the cone of light. If it is 

 too large for the specimen, either the lamp condenser is too near the 

 radiant or the specimen is too close to the lamp condenser. (Fig. 210.) 



If one uses a substage condenser it and the lamp condenser should 

 be so placed that the entire cone of light traversing the lamp condenser 

 can enter the substage condenser. If the cone is too large they are 

 too close together, or the lamp condenser is too near the radiant. If 

 the cone is too small then the lamp condenser is too far from the 

 radiant or the substage condenser, or perhaps both faults are present. 

 One must remember in all his experiments that a converging cone of 



