25 
*Test-plate after Abbe — for testing the spherical and 
chromatic aberration of objectives, and for estimating the 
thickness of cover corresponding to the most per- 
fect c o r r e c t i o n. Six cover-glasses, having the exact thickness 
Fig. 3. 
Test-plate No. 3. 
marked on each (0.09 to 0.24 mm), cemented in succession on a 
slip, their lower surface silvered and engraved with parallel lines, 
the contours of which form the test. For use with the Abbe 
Condenser (see Instruction for use). In case 10. 
