CH. VI] MICRO-SPECTROSCOPE AND POLAR/SCOPE 141 



end prisms of crown glass cause the rays to emerge approximately parallel with 

 the axis of the microscope. A single ray is represented as entering the prism and 

 this is divided into three groups (Red, Yellow, Blue), which emerge from the 

 prism, the red being least and the blue most bent toward the base of the flint prism 

 (see Fig. 124'!. 



Hinge. — The hinge on -which the prism tube turns when it is swung off the 

 ocular. 



Ocular (I iSS) — The ocular in which the slit mechanism lakes the place of the 

 diaphragm (§ 19S). The eye-lens is movable as in a micrometer ocular, so that 

 the slit may be accurately focused for the different colors (\ 200). 



S. Screw for setting the scale of wave lengths ( \ 202). 



S' . Screw for regulating the width of the slit ( \ 19S). 



S" '. Screw for clamping the micro-spectroscope to the tube of the microscope. 



Scale Tube. — The tube near the upper end containing the Angstrom scale and 

 the lenses for projecting the image upon the upper face of the Amici prism, whence 

 it is reflected upward to the eye with the different colored rays. At the right is a 

 special mirror for lighting the scale. 



Slit. — The linear opening between the knife edges. Through the slit the light 

 passes to the prism. It must be arranged parallel with the refracting edge of the 

 prism, and of such a width that the Fraunhofer or Fixed lines are very clearly and 

 sharply defined when the eye-lens is properly Jocused ('',. 198-200). 



Stage. — The stage of the microscope. This supports a watch-glass with sloping 

 sides for containing the colored liquid to be examined. 



(3) Comparison Prism with tube for colored liquid (C. I.), and mirror. The 

 prism reflects horizontal rays vertically, so that when the prism is made to cover 

 part of the slit two parallel spectra may be seen, one from light sent directly through 

 the entire microscope and one from the light reflected upward from the comparison 

 prism. 



(4) View of the Slit Mechanism from below. — Slit, the linear space between 

 the knife edges through which the light passes. 



P. Comparison prism beneath the slit and covering part of it at will. 



S. S' . Screws for regulating the length and width of the slit. 



Fig. 124. Flint-Glass Prism showing the separation or dispersion of white 

 light into the three groups of colored rays (Red, Yellow, Blue), the blue rays being 

 bent the most from the refracting edge (\ 189). 



Fig. 125. Sectional View of a Microscope with the Polariscope in position 

 ($218-227). 



Analyzer and Polarizer. — They are represented with corresponding faces par- 

 allel so that the polarized beam could traverse freely the analyzer. If either Nicol 

 were rotated 90 they would be crossed and no light would traverse the analyzer 

 unless some polarizing substance were used as object, (a) Slot in the analyzer 

 tube so that the analyzer may be raised or lowered to adjust it for difference of 

 level of the eye-point in different oculars ( \ 59, 200). 



Pointer and Scale. — The pointer attached to the analyzer and the scale or divided 

 circle clamped (by the screw S) to the tube of the microscope. The pointer and 

 scale enable one to determine the exact amount of rotation of the analyzer (\ 220). 



Object — The object whose character is to be investigated by polarized light. 



