CH. IX] BLACK APPARATUS FOR MICRO-PROJECTION 



243 



properly and has ill success in general, there is no wonder, as he has 

 blinding reflections constantly in his eyes. With a dull black finish 

 for all outside surfaces, if the apparatus is properly built, this 

 defect will be abolished. Polished black finish will not answer, for 

 it reflects almost perfectly. The finish must be dull, dead, or luster- 

 less, then the light will be mostly absorbed, and so small a part 

 reflected that no inconvenience is produced. 



371. Blackening the interior of projection apparatus. As 



with the exterior of projection apparatus, so the interior of all the 

 parts should be dull black to avoid internal reflections and conse- 

 quent confusion. This is especially true of the objective mount- 

 ings, the tube of the microscope and the amplifier tube. Lewis 



FIG. 137. DIAGRAM TO SHOW THE SIZE OF IMAGE WITH THE SAME OBJEC- 

 TIVE AND DIFFERENT LENGTH AND DIAMETER OF MICROSCOPE TUBE. 



Objects The different lengths of object shown. 



Objective The projection objective. 



Microscope Tube Microscope tubes with diameters of 48, 30 and 23 milli- 

 meters. 



i, 2 Rays which are stopped by the largest tube. 



Ray 3 The marginal ray allowed to pass by the largest (48 mm.) tube. 



Ray 4 The extreme marginal ray allowed to pass by the 30 mm. tube. 



Ray 5 The marginal ray allowed to pass the 23 mm. tube. 



Axis The optic axis. 



Images The one in full lines is for the smallest tube. The others in 

 broken lines for the tubes of larger size. 



By tracing back to the specimen it is seen that the larger tubes show corre- 

 spondingly more of the object, the projection objective remaining the same. 



