II. SELECTORS. 211 



833. Large Spectroscope, according to Meyerstein's system 

 for determining the relations of refraction and dispersion of diffe- 

 rent media, with contrivance for polarisation. 



Schmidt and Haensch, Berlin. 



834. Smaller Spectroscope, of the exhibitors' own con- 

 struction. Schmidt and Haensch, Berlin. 



835. Spectroscope, according to Abbe's system, with divi- 

 ded circle of 20 cm. diameter, repeating circle, and micrometer 

 apparatus for determining the dispersion. Also a hollow prism 

 with metal body. Carl Zeiss, Jena. 



The spectroscope has only one telescope, which serves at the same time 

 for collimation and observation. The adjustment brings about automatically 

 the minimum deviation for every ray. The measurement of the refracting 

 angle and that of the deviation takes place without change in the instrument. 

 The determination of the dispersion is effected, independently of ascertaining 

 the absolute refractive index of one colour, by micrometric measurement. 



836. Two Prisms of Glass, for observing the dispersion 



of coloured liquids ; constructed by Steinheil, of Munich. 



Prof. Kundt, Strassburg. 



The refracting edge of the hollow prisms is so sharp that they show the 

 dispersion of even highly coloured liquids. 



837. Spectroscope, with five-inch circle, according to Dr. 

 Meyerstein's system, for measuring the refraction and dispersion 

 of different media, for chemical and optical analysis, as well as for 

 all kiuds of goniometrical measurements. 



There are belonging to this : 



a. Small circle with pivot and plate. 



b. Telescope with stand. 



c. Slit tube (Spaltrohre). 



d. Scale tube. 



e. Crystal stand. 

 /. Prism. 



Aug. Becker (Dr. Meyer steirfs Astronomical and Physical 



Workshops}^ Gottingen. 



The telescopes, when required, are screwed on to the places marked 

 " Fernrohre," " Spaltrohre," &c. The small circle is put into the middle of the 

 larger one. To determine the refracting angle of a prism, the telescope is 

 attached to that part of the instrument which is marked " Zur Bestinmung, 

 &c.," it is left here for all goniometric measurements, but the smaller circle is 

 removed and the crystal-holder put into its place. 



838. Spectroscope, of the latest construction, according to 

 Dr. Meyerstein's system, arranged for the relations of refraction 

 and dispersion of different media, for the reflection of polarised 

 light at the free surface of liquids, as well as for the reflection of 

 solid bodies, for all kinds of goniometrical measurements, and for 

 chemical and optical analysis. 



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