CH. VI] MICRO-SPECTROSCOPE AND POLAR/SCOPE 163 



emerge from the prism, the red being least and the blue most bent toward the 

 base of the flint prism (see Fig. 139). 



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

 ocular. 



Ocular ({S 2 to) — The ocular in which the slit mechanism takes the place of 

 the diaphragm (J220). The eye-lens is movable as in a micrometer ocular, so 

 -that the slit may be accurately focused for the different colors (\ 222). 



5. Screw for setting the scale of wave lengths (\ 224). 



S' '. Screw for regulating the width of slit (§220). 



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

 scope. 



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 Amiciprism, 

 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 focused (\ 220-222). 



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. L.), 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. 139. 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 (\ 211). 



Fig. 140. Sectional view of a Microscope with the Polariscope in position 

 (g 240-242). 



Analyzer and Polarizer. — They are represented with corresponding faces 

 parallel 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 (jj 67,222). 



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 (\ 242). 



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



