158 



Spectacles, Mydriasis. Spectacles with blackened discs pierced 

 with small holes for testing chronic dilatation of the pupils. 

 [26.} 



Spectacles, Periscopic. Spectacles having concavo-convex lenses 

 with their curvature nearly parallel with the cornea. [20, 

 21, 26.] 



Spectrpgraph. An instrument, consisting essentially of a com- 

 bined prism spectroscope and camera, for producing, 

 observing and photographing spectra. [14, 26.] 



Spectre-graph, Concave Grating. A spectrograph in which a 

 Rowland concave grating is used instead of a prism to 

 produce the spectrum. 



Spectrograpb, F6ry. A spectrograph in which the collimator and 

 camera lenses are entirely suppressed, the only optical work 

 being the prism itself. 



Spectrograph, Quartz. A spectrograph in which all the optical 

 parts (prisms and lenses) are made of quartz to allow ultra- 

 violet light to be transmitted. [2, 10, 11, 14, 26.] 



Spectrograph, Quartz, "Arc" Form. A quartz spectrograph 

 in which the camera arm is supported by a solid arc with 

 divisions for setting. 



Spectrograph, Quartz, Littrow. A quartz spectrograph specially 

 designed to give a widely-dispersed spectrum with com- 

 pactness of the instrument. 



Spectrograph, Ultra-Violet Glass. A spectrograph with prisms 

 and lenses of glass for photographing a portion of the ultra- 

 violet spectrum. [14, 26.] 



Spectroheliograph. For producing a monochromatic photo- 

 graph of the sun's disc. [4, 11, 13, 14, 26.] 



Spectrometer. A prism spectroscope (q.v.) fitted with divided 

 circle, etc., for the accurate measurement of angles and the 

 determination of wave-lengths of spectra. [2, 13, 14, 19, 

 26.] 



Spectrometer, Hilger Wave-Length. A spectrometer in which 

 the collimator and telescope are fixed and a constant devi- 

 ation prism is rotated. The wave-lengths are read off direct 

 on a drum attached to the screw rotating the prism table. 

 [14.] 



Spectrometer, Infra Red. A spectrometer with mirrors, rock- 

 salt prism and thermopile for the examination of the non- 

 luminous infra red portion of the spectrum. [14.] 



Spectrometer, Wave-Length. A spectrometer in which wave- 

 lengths are measured by means of a photographic scale, the 

 reflected image of which is seen in the telescope in juxta- 

 position to the spectrum. [14.] 



Spectrophotometer. An instrument for comparing and com- 

 pounding the colours of the spectrum. [14.] 



Spectroscope. An instrument for the production and examina- 

 tion of spectra or absorption phenomena. It consists 

 essentially of a collimator with adjustable slit to transmit a 



