214 SEC. 7. LIGHT. 



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

 a diaphragm instead of cross threads for measurement of position 

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



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

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

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

 This spectroscope 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 otherwise. 



851. Spectroscope, with compound prism and angular scale. 



Yeates Sons. 



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



853. Three Foucault's Prisms. 



Iceland-spar, cut in three directions. 



Small rhombohedron of Iceland 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. 



Prism of crown glass. 



Two polyprisms (glass). 



One poly prism (quartz). 



Collection of nine prisms. 



Boscowich prisms. 



Fresnel's tri-prism. 



Fresnel's Parallelepipeds, mounted in brass. 



Laurent, Paris. 



854. Prisms for direct Vision in 3 pieces. 



J? >? ?5 ** V 



>j ;? >? 



Kochon prism. 

 Wollaston prism. 



(small). 



Achromatized Iceland spar prism. 

 Cube of fluor-spar. 

 Fluor-spar lens. 



Cemented cells for spectroscopic work (9). 

 Tubes with platinum wire (6). 

 Collection of quartz and Iceland spar prisms. 

 Spectroscope with one prism, one and two burners. 

 Object-glass for projecting ray spectra. 



Laurent, Paris. 



