184 S.EC. 7. - LIGHT. 



846. Pocket Spectroscope of the simplest and cheapest 

 kind. A. Hilger, London. 



847. Two perfect Bight-angle Prisms. A. Hilgcr. 



848. Nicol and a Double Image Prism. A. Hilger. 



849. Spectroscope made by Yeates, of Dublin, fitted with 

 a diaphragm instead of cross threads for measurement of position 

 of lines. Professor Jos. P. O'Reilly. 



The diaphragm, above, being perfectly opaque, is always risible against 

 even the faintest lines ; moreover, it dispenses with the introduction of an 

 extraneous light which may by its brilliancy interfere with .that of faint lines. 

 This spectroscopte is specially adapted for the examination of fluorescent 

 minerals, the prisms and lenses being of quartz. 



850. Spectroscope, with bi-sulphide of carbon prisms and 

 lens, arranged for projection. Yeates $ Sons. 



The prisms and collimating lens are so proportioned that no light is lost 

 by passing outside the prisms or othenvise. 



851. Spectroscope, with compound prism and angular scale. 



Yeates fy Sons. 



852. Spectroscope, with two prisms. James How fy Co. 



853. Three Foucault's Prisms. 



Fluor-spar, cut .in three directions. 



Small rhombohedron of fluor-spar. 



Cone and pyramid (black) for Guerard's apparatus. 



Cone for the projection of annular spectrum. 



Pyramid for the projection of four spectra. 



M. Mascart's prism. 



Small prism of crown glass. 



Two polyprisms (glass). 



One poly prism (quartz). 



Collection of nine prisms. 



Boscowich prisms. 



Fresnel's tri-prism. 



Laurent (Paris). 



854. Prisms for direct Vision in 3 pieces. 







Rochon prism. 

 Wollaston prism. 



(smaU). 



Fluor-spar prism. 

 Cube of fluor-spar. 

 Fluor-spar lens. 



Three cells for spectroscopic work. 

 A collection of quartz and fluor-spar prisms. 

 Spectroscope with one prism. 

 Object-glass for projecting ray spectra. 



Laurent. 



