218 6EC. 7. LIGHT. 



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, aKso 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 Sac char ometer, with 

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

 meter. Laurent, Paris. 



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

 model). M. J. Duboscq, Paris. 



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



M. J. Duboscq, Paris. 



86 Id. Large Circle for measuring the elements of elliptic 

 and rotatory polarisation in solids and liquids, and reproducing 

 all impressions of polarisation 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 9 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. Wilhelin Albert, Frank for t-on- Maine. 



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

 J. Mullens Lehrb. der Phys., 7 Aufl., I. Bd., 3tes. Buch, caps. 9 and 10." 



867. Polarising Apparatus, for projection with rotatory 

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

 undulation plate. (Comp. Poggendorff's Ann., 1875, No. 12.) 



J. Wilhelm Albert, Frankfort-on- Maine. 



The ray of sun or electric lamp falls through a Nicol, which is protected 

 with a shade, upon a press, in which the object is fastened by means of spring 

 clamps, and passes thence through a tube which can be rotated with great 

 velocity. This tube is provided at one end with a shade capable of rotating 



