CH. IX] MICRO-PROJECTION WITH DIRECT CURRENT 239 



The metal lamp-house is semi-transparent as it was in position during only 

 a part of the exposure for the photograph. 



The condenser and water-cell are connected to the stage by a bellows to 

 exclude stray light. 



The microscope shows the objectives on a revolving nose-piece and behind 

 them a metal shield to keep stray light from the screen. 



An amplifier is shown in place, at the end of the large tube of the microscope. 



The arc lamp, condenser, stage and microscope are each on an independent 

 block which moves along the optical bench on the single baseboard. The 

 vertical white lines on the baseboard indicate the position of the various blocks 

 for the optical combination here shown. 



On the front legs of the table is the adjustable drawing shelf upon which are 

 demonstration preparations. 



The scale of this picture is shown by the 10 centimeter rule just above the 

 table drawer at the right. 



of the spectrum and thus helps to avoid the overheating which 

 would result if all of this energy remained. The best position of 

 the water-cell is between the first and second elements of the con- 

 denser, where the rays are practically parallel (fig. 121). For 

 further discussion of the avoidance of heating the specimens, see 

 852. 



365. Stage for specimens. The stage should be of ample 

 size, and should have an opening sufficiently large for the largest 

 specimens to be used in micro-projection, that is, not less than 65 

 mm. (2 l /2 in.) square. 



366. Mechanical stage. If serial sections are to be used 

 with the apparatus then the stage should be supplied with a 

 mechanical stage of great range, that is about 50 x 65 mm. This 

 is about the maximum range for the sections mounted on slides 

 50 x 75 mm. (2x3 in.) (fig. 135, 136). , 



367. Stage cooling device. While the large water-cell in 

 connection with the condenser absorbs practically all the long 

 waves of radiant energy that can be absorbed by water, it is very 

 desirable, and for many specimens necessary, to have some device 

 for carrying off the heat developed in the specimen itself by the 

 absorbed light. The most practical stage cooling device is a stage 

 water-cell. The one found very efficient and satisfactory in every 

 way is shown in fig. 121, 134. The specimen rests directly against 

 the glass side of the water-cell and is cooled bv conduction. Manv 



