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1 86 DRAWING WITH A PROJECTION MICROSCOPE [Ch. VI 



varying the distance between the objective and the drawing surface, 

 and consequently the scale of the drawing (for erect images see § 277- 



284). 



§ 296. Drawing with objectives of 25 to 10 mm. focus. — For this 



the best way is to use a three lens condenser, as shown in fig. 109, in, 



and for a microscope use 

 either the special water- 

 cell stage or the ordinary 

 microscope with large 

 tube. For radiant use a 

 small or a large arc lamp. 

 Remove the substage con- 

 denser or turn it aside and 

 arrange on the optical 

 bench so that the image 

 of the light source from 

 the large condenser falls 

 directly on the specimen. 

 Focus and arrange the 

 drawing surface to give 

 the right size and mag- 

 nification, then trace the 

 outlines and the details. 

 Later, ink in, using the 

 specimen to check up with 

 (for erect images see § 277— 

 284). 



Fig. 112. Projection Microscope with Mov- 

 able Drawing Table and 45° Mirror. 



(From Optic Projection). 



The projection table has the dimensions given 

 in fig. 109. 



The arc lamp is automatic and the rheostat 

 for current varying from 10 to 20 amperes. 



The condenser is of the three lens water cell 

 type, and the microscope with separate stage; 

 the microscope has an amplifier in place. 



The drawing table (Dr. Table) is of a conven- 

 ient height for sitting beside. It is 76 cm. high 

 and the top 100 cm. long and 75 cm. wide. 



The 45 plate glass mirror is large (75 cm. long 

 and 60 cm. wide). 



After one has had sufficient practice, the drawing can be partly 

 or wholly completed under the projection apparatus. For this one 

 must light the drawing surface enough either by means of a portable 

 lamp or by some means of letting in daylight. At the same time 

 there must be a screen to cut off the image where one is doing the 

 finishing. By removing the screen the image appears at any time 

 and serves to check the work. 



§ 297. Drawing with high powers, 8 to 2 mm. focus. — For this 

 high power drawing one should use an ocular as well as an objective, 



