CH. IX a\ PROJECTION MICROSCOPE 263 



light should be used and not a diverging one. The specimen must 

 then not be beyond the focus of the lamp condenser. 



417. Centering and Serial Arrangement. In installing a 

 projection apparatus like the one in Fig. 204, one can get the proper 

 adjustments first by making careful measurements. That is the upper 

 carbon should be opposite the center of the lamp condenser, and the 

 objective should also be in line with the center of the lamp condenser. 

 By moving the condenser close to the lamp and raising the carbon in 

 the position occupied when in actual use one can get the end opposite 

 the axis of the condenser by mutually adjusting lamp and condenser. 

 Then by removing the stage the microscope may be brought close to 

 the condenser and raised or lowered until the objective is opposite the 

 center. The stage should then be put in position and adjusted so that 

 the center shall be opposite the objective. 



The purpose of all this is to get all the pieces centered to one axis. 

 If now the current is turned on the slight adjustments necessary for 

 the final centering may be made by the centering screws of the lamp 

 (Fig. 205 D (C D) ). 



The relative position of the various pieces in a projection micro- 

 scope along the axis can be determined only by trial. If one remem- 

 bers that the object is to be illuminated by a converging cone of light 

 it will aid in getting the parts in the right position. Firstly the lamp 

 condenser must be at the right distance from the radiant. Fig. 210 

 shows the appearances in an ordinary magic lantern with the different 

 relative positions of radiant and condenser. For the condenser here 

 used (Fig. 204) the crater in the upper carbon should be about 8 cen- 

 timeters from the mica sheet over the condenser. One can determine 

 this only by trial. By changing the relative position of condenser to 

 radiant and the object to the condenser, and then the objective and 

 object one can find the positions giving the most satisfactory results. 

 When these are found it is worth while, as shown in the picture, to 

 make lines on the fixed part of the apparatus indicating them. A 

 study of Fig. 209 will aid one in understanding the principles involved 

 in the best relative positions. The actual cone of light from the con- 

 denser will be easily seen if some dust, like that from a blackboard 

 eraser is diffused in the air near the front of the condenser. 



If a lamp condenser is properly constructed there is no necessity 

 of using a special substage condenser if the different parts are freely 

 movable. If, however, one must put the object in the same position 



