II, SELECTOKS. 185 



854a. Collection of Prisms, for optical purposes. 



Laurent^ Paris. 



854b. Spectroscope. M. J. Duboscq, Paris. 



854c. Prisms, by Arago. Paris Observatory. 



854d. Prisms, by Borda. Paris Observatory. 



854e. Collection of Compounds of Silicon with various 

 Metals for optical purposes. Feil, Paris. 



1 . Disc of Crown Glass, 4 inches. 



2. Disc of Flint Glass, 4 inches. 



3. Plate of Crown Glass (heavy English). 



4. Parallelepiped, of ordinary flint glass. 



5. Crown Glass Prism. 



6. Flint Glass Prism. 



7. Flint Glass Prism, (sp. gravity 4*4.) 



7a. Prism manufactured by Fraunhaufer Guinand. 



8. Flint Glass Prism (very heavy), sp. gr. 4 4. 



9. Flint Glass Prism, sp. gravity 4. 



10. Flint Glass Prism, sp. gravity 5 2. 



11. Flint Glass Prism, sp. gravity 5'5; samples by the dry 



method. 

 11 a. Silicate of Potassium and Calcium with Titanium. 



12. Aluminate of Silicium and Magnetism. 



13. Crystallisation of Alumina and Magnesia. 



14. Crystallisation of Fluosilicate of Magnesium and Calcium. 



15. Alumina and Magnesia Crystallised by Fluosilicate of 



Potassium. 



16. Crystallisation of Fluosilicate of Aluminium. 



17. Crystallisation of Barosilicate of Aluminium. 



18. Crystallised Aluminate of Magnesium and Silicium. 



19. Manufacture of Adamantine Boron. 



20. Plate of Crystals of Aluminium. 



21. Blue Obsidian. 



22. Obsidian coloured by Cobalt. 



23. Samples of Crown Glass, extra white. 



854f. Objective of Bock Crystal, 10 centimetres in dia- 

 meter. M. Liitz, Paris. 



854g. Astronomical Glasses, for cabinets of physics. 



M. Lutz, Paris. 



855. Micro-spectroscope. Spectral ocular with prism for 

 comparing two spectra, and with Abbe's measuring apparatus for 

 the direct estimation of the wave lengths of dark or bright lines in 

 a spectrum. In case. C. Zeiss, of Jena. 



This spectroscope gives the position of the bright or dark lines by means 

 of a scale on which the spectrum is thrown, and which, by means of its peculiar 



