CHAPTER VI. 



MICRO-SPECTROSCOPE AND POEARISCOPE. 



APPARATUS AND MATERIAI, REQUIRED FOR THIS CHAPTER. 



Compound microscope ; Micro-spectroscope (§ 179) ; Watch-glasses and small 

 vials, slides and covers (<j 198) ; Various substances for examination (as blood and 

 ammonium sulphide, permanganate of potash, chlorophyll, some colored fruit, 

 etc., (§ 199-209) ; Micro-polarizer ($ 211) ; Selenite plate ($ 220) ; Various doubly 

 refracting objects, as crystals, textile fibers, starch, section of bone, etc. 



MICRO-SPECTROSCOPE. 



\ 179. A Micro-Spectroscope, Spectroscopic or Spectral Ocular, is a direct vision 

 spectroscope in connection with a microscopic ocular. The one devised by Abbe 

 and made by Zeiss consists of a direct vision spectroscope prism of the Amici pat- 

 tern, and of considerable dispersion, placed over the ocular of the microscope. 

 This direct vision or Amici prism consists of a single triangular prism of heavy flint 

 glass in the middle and one of crown glass on each side, the edge of the crown 

 glass prisms pointing toward the base of the flint glass prism, i. e., the edges of the 

 crown and flint glass prisms point in opposite directions. The flint glass prism 

 serves to give the dispersion or separation into colors, while the crown glass prisms 

 serve to make the emergent rays approximately parallel with the incident rays, so 

 that one looks directly into the prism along the axis of the microscope. 



The Amici prism is in a special tube which is hinged to the ocular and held in 

 position by a spring. It may be swung free of the ocular. In connection with 

 the ocular is the slit mechanism and a prism for reflecting horizontal rays verti- 

 cally for the purpose of obtaining a comparison spectrum ($ 192). Finally near 

 the top is a lateral tube with mirror for the purpose of projecting an Angstrom 

 scale of wave lengths upon the spectrum (§ 193, Figs. 1 13-114). 



\ 180. Apparent Reversal of the Position of the Colors in a Direct Vision Spec- 

 troscope. — In accordance with the statements in \ 179 the dispersion or separation 

 into colors is given by the flint glass prism or prisms and in accordance with the 

 general law that the waves of shortest length, blue, etc., will be bent most, conse- 

 quently the colors have the position indicated in the top of Fig. 117, also above 

 Fig. 118. But if one looks into the direct vision spectroscope or holds the eye close 

 to the single prism (Fig. 118), the colors will appear reversed as if the red were 

 more bent. The explanation of this is shown in Fig. 118, where it can be readily 

 seen that if the eye is placed at E, close to the prism, the different colored rays 



