CH. IX] 



HIGH POWER MICRO-PROJECTION 



277 



Finally if one uses a main condenser with a focus of 30 or 38 cm. 

 (12 to 15 in.) excellent results can be obtained with all powers (16 

 to 2 mm.) by so placing the microscope that the converging cone of 

 the main condenser shall enter the substage condenser at a point 

 where the light cone is of about the diameter of the substage con- 

 denser (fig. I54A-B). It may be necessary to raise or lower the 

 substage condenser slightly to obtain the most brilliant screen 

 image. 



Fair results can also be obtained in this way by using main con- 

 densers of 15, 20 and 25 cm. (6, 8, 10 in.) focus, but much more 



Substage 

 Condenser 



FIG. 154. 



DIAGRAMS TO SHOW THE POSITION OF THE SUBSTAGE CONDENSER 

 WHEN NO PARALLELIZING LENS is USED. 



A The substage condenser is within the focus (/) at a point where the long, 

 light cone is of about the same diameter as the substage condenser. 



B The substage condenser is beyond the focus (f) of the long focus main 

 condenser, at a point where the diverging cone is of alaout the same diameter as 

 the substage condenser. This is the better position for the s.ubstage condenser 

 of the ordinary microscope. 



Arc Supply The right-angled carbons of the arc lamp. 



L r L 2 The first and the second elements of the main condenser. 



Water Cell This is to remove the radiant heat. 



Axis The principal axis on which all the parts are centered. 



/ The principal focus of the second element of the main condenser. In both 

 cases the focus is long as compared with fig. 153. 



Substage Condenser This is the first or lowest element of the substage con- 

 denser. It is of the achromatic type (fig. 150 A). See figure 150 B for 

 the Abbe form of substage condenser with parallel and with converging light. 



