Xo. 158. Diffraction Apparatus. Constructed by ABBE in 1876 it 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 only adapted for the ob- 

 jective aa. 



No. 15!). Diffraction Plate. This plate consists of a glass slide 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. 



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

 kroskop", vol. I, pp. 147 156; ZIMMERMANN, "Das Mikroskop", Vienna, 1895, 

 pp. 46 ; f)l. 



1= 



D. Appliances for microscopic examination 

 in polarised light. 



Nos. 160 and 161. Polarisers. As a rule we supply polarisers with end- 

 surfaces inclined to the optical axis of the microscope. That having an aperture 

 of 10 mm, Polariser I, No. 160, is intended for use with Stands I, III and IV. 



Selenite and mica films may be placed upon the plate-shaped rim of the mount. 



The other form of 8 mm aperture, Polariser II, No. 161, is as a rule 

 supplied only for use with the double-lens condenser system, num. Ap. 1.0 for 

 Stand VD. 



The iris-diaphragm No. 3810 of the simplified illuminating apparatus No. 3805 

 (see pp. 3; and 54) can in Stand V D be inserted between the condenser system 

 and Polariser II. 



In subsequent ordering Polariser 

 number of the Stand should be stated. 



II, No. 161, the factory 



