100 



model the glass disk is mounted upon a metal plate with a slot for the more 

 certain and more convenient adjustment of the indices. 



Prices : Code-words : 



No. 155: Simple Apertometcr, in case ....... Marks jo. . Pelar. 



,, 156: Apertometer with slot to guide movement of indices go. . Pelaza. 



* ABBE's TestrPlate. 



A Test -plate for testing lenses with respect to spherical and chromatic 

 aberrations and for estimating that thickness of the cover-glass which corresponds 

 to the most perfect correction was designed by Professor ABBE in 1873. Used 

 in conjunction with the ABBE Illuminating -apparatus and by establishing the 

 so-called sensitive rays, it gives the greatest prominence to any existing faults 

 of correction. 



This test-plate consists of an object carrier with six cover-glasses of accura- 

 tely determined thickness (0.09 mm to 0.24 mm) cemented side by side. These 

 cover -glasses are silvered on their lower surfaces and engraved with lines, the 

 serrated edges of which form the test-object proper. 



No. 157: ABBE's Test-plate, in case . . Price; Marks w. . Code- word: Peleador. 



See "Archiv f. mikr. Anat", vol. IX, 1873, pp. 434437; also DIPPEL "Das 

 Mikroskop", vol. I, p. 340, and the directions accompanying the test-plate. 



* ABBE's Diffraction Apparatus, 



The Diffraction Apparatus perfected by Professor ABBE in 1876 serves 

 to demonstrate the effects of diffraction in the formation of microscopical images. 

 It consists of a diffraction-plate and a set of stops, with an arrangement for 

 fitting and rotating them above the objective. The dimensions of the stops are 

 such as to adapt them for objective aa. 



The diffraction - plate consists of a glass slip with three cover - glasses 

 cemented side by side. The lower surfaces of the latter are silvered and have 

 groups of lines ruled upon them so as to form various simple and crossed gratings. 



Prices : Code- words : 



No. 158: Diffraction Apparatus Marks 20. . Pelele. 



,, 159: Diffraction-plate separately, in case ,, 8. . Pelicabra. 



See "Monthly Micr. Journ.", vol. XVII, 1877, pp. 8288; DIPPEL "Das Mi- 

 kroskop", vol. I, pp. 147156; ZiMMERMANN "Das Mikroskop", Vienna, 1895, 

 pp. 4651. 



