182 SEC. 7. LIGHT. 



change in the instrument. The determination of the dispersion is effected, 

 independently of ascertaining the absolute refraction index of one colour, by 

 micrometric measurement of the angle. 



836. Two Prisms of Glass, for observing the dispersion 



of coloured liquids ; constructed by Steinheil, of Munich. 



Professor Kundt, Strassburg. 



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

 dispersion of even highly coloured liquids. 



837. Spectrometer, 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 kinds of gouiometrical measurements. 



There are belonging to this : 



a. A small circle with pivpt and plate. 



b. A telescope with stand. 



c. A slit tube (Spaltrohr). 



d. A scale tube. 



e. A crystal stand. 



f. A prism. 



Aug. Becker (Dr. Meyer stein 1 s Astronomical and Physical 



Workshops), Gottingen. 



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

 " Fernrohr," " Spaltrohr," &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. Spectrometer, 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. 



There are belonging to this : 



a. A small circle with plate. 



b. Two telescopes. 



c. Two slit-tubes (Spaltrohre). 



d. One scale-tube. 



e. A Babinet's compensator. 



f. Two weights for balancing telescope and split in a vertical 



position. 



g. A crystal stand. 



h. A flint-glass prism. 



Aug. Becker (Dr. Meyerstein's Astronomical and Physical 



Workshops] , Gottingen. 



For attaching the telescopes, collimators, &c., the same rules apply as 

 in the previous case. The larger telescope and collimator serve for deter- 



