II. SELECTORS. . 187 



b. POLARISCOPES, &C. 



861. Jellett's Saccharometer, for the measurement of the 

 rotation which certain fluids are capable of producing in the plane 

 of polarisation of the transmitted ray. Rev. John H. Jellett. 



This rotation is measured by the method of compensation, the original 

 position of the plane being restored by transmission through a column of fluid 

 possessing an opposite rotatory power. This fluid is contained in a vessel 

 closed at the bottom with glass, and the length of the column is regulated by 

 means of a tube, also closed with glass, which is capable of moving in the 

 direction of its axis, the amount of this movement being read off on a scale. 



A full description of the instrument and of the analysing prism used in its 

 construction is given in the " Transactions of the Royal Irish Academy," 

 Vol. XXV., pp. 373-82. 



86 la. Laurent Polarimeter and Saccharometer, with 

 two divisions on the plate, with inversion tube and one thermo- 

 meter. Laurent, Pans. 



86 Ib. Saccharometer, by Soleil, with penumbra (large 

 model). M. J. Duboscq, Paris. 



861c. Large Circle, by Messrs. Jamin and Senarmont. 



M. J. Duboscq, Paris. 



86 Id. Large Circle for measuring the elements of elliptic 

 and rotatory polarization in solids and liquids, and reproducing 

 all impressions of polarization and refraction. (This apparatus 

 belongs to the School of Photography.) M. Lutz, Paris. 



862. Polarising Apparatus, according to Dove's system, 

 complete, with polyoscope and dichroscope. 



Schmidt and Haensch, Berlin. 



863. Simple, handy Polarising Apparatus, according to 

 Carl's system. Schmidt and Haensch, Berlin. 



864. Melde's Models, for illustrating the colours of thin 

 leaves in polarised light. Ferdinand Suss, Marburg. 



865. Melde's Model, for illustrating circular polarisation 



by means of gypsum and scales of mica. 



Ferdinand Suss, Marburg. 



866. Paste-board Models, according to J. Miiller's system, 

 for illustrating the colour phenomena in polarised light, 

 and the uni-axial and bi-axial crystals. 



J. Wilhclm Albert, Frankf or t-on- Maine. 



Ten models of cardboard, together with a treatise on them. Described in 

 J. Miiller's "Lehrb. der Phys., 7 Aufl., I. Bd., Stes. Buch, caps. 9 and 10." 



867. Polarising Apparatus, for projection with rotsilory 

 analyser, according to E. Mack's system, with quartz plate and 

 undulation plate. (Comp. PoggeudorfFs Ann., 1875, No. 12.) 



J. Wilhelm Albert, Frankf or t-on- Maine. 



