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SPECTRAL EYE-P 



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47 





c. The Spectral Eye-piece. 



Microspectral apparatuses have been recently made, which not 

 only serve for the investigation of microscopic objects, but have 

 also proved useful for other spectro-analytical researches. They 

 consist of arrangements to be 

 applied to the eye-piece of the 

 Microscope, and may therefore 

 be termed spectral eye-pieces. 



The best apparatus of this y 

 kind is that constructed by 

 John Browning, of London, 

 after his own design and that 

 of Mr. Sorby. It consists of 

 an ordinary eye-piece, of which 

 the tube a (Fig. 13) fits into 

 the body-tube. Between the 

 field-lens n and the eye-lens 

 m is a prism p, which lies in 

 contact with the diaphragm s. 

 The diaphragm is in the form 

 of a slit, which may be dimin- 

 ished in length or breadth by 

 a special contrivance. At the 

 side is an opening o, through 

 which the light from the objects serving for comparison-spectra 

 falls upon the prism and is totally reflected through the series of 

 prisms above to the eye of the observer at o. This apparatus may 

 be used for observing the spectrum of the Algte chlorophyll-green 

 placed on the microscope-stage, and simultaneously the comparison- 

 spectrum of a solution of chlorophyll in alcohol in a small test- 

 tube placed in front of the aperture at o' on a specially devised 

 stage. 



The analyzing prism is applied above the eye-lens m, and is 

 removable; it is composed of two flint- and three crown-glass 

 prisms, and acts in such a manner that the light reaches the eye 

 in a direction parallel to the axis. If we look through this prism 

 down the Microscope in ordinary daylight, and adjust the opening 

 of the diaphragm properly, a spectrum of unusual clearness and 

 brilliancy is seen, in which the lines from B to G appear with 



FIG. 13. 



