CHAPTER IV. 



MICRO-SPECTROSCOPE AND POLARISCOPE. 



APPARATUS AND MATERIAL REQUIRED FOR THIS CHAPTER. 



Compound microscope (Ch. I) ; Micro-spectroscope (_§ 128) ; Watch-glasses and 

 small vials, slides and covers (gg 143, 144) ; Various substances for examination 

 (as blood and ammonium sulphide, permanganate of potash, chlorophyll, some 

 colored fruit, etc. (§§ 144-145) ; Micro-polarizer (| 150) ; Selenite plate (§157 f.) ; Var- 

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



MICRO-SPECTROSCOPE. 



§ 128. — 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 pattern, and of considerable dispersion, placed over the ocular of the micro- 

 scope. 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 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 (g 137). Finally near 

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

 scale of wave lengths upon the spectrum ($ 138). 



$ 129. Various Kinds of Spectra. — By a spectrum is meant the colored bauds 

 appearing when light traverses a dispersing prism or a diffraction grating, or is af- 

 fected in any way to separate the different wave lengths of light into groups. 

 When daylight or some good artificial light is thus dispersed one gets the appear- 

 ance so familiar in the rain-bow. 



{A) Cofitinuous Spectrum. — In case a good artificial light or the electric light is 

 used the various rain-bow or spectral colors merge gradually into one another in 

 passing from end to end of the spectrum. There are no breaks or gaps. 



(B) Line Spectrum. — If a gas is made incandescent the spectrum it produces 

 consists, not of the various rain-bow colors, but of sharp, narrow, bright lines, the 

 color depending on the substance. All the rest of the spectrum is dark. These 

 line spectra are very strikingly shown by various rnetals heated till they are in 

 the form of incandescent vapor. 



(C) Adsorption Spectrum. — By this is meant a spectrum in which there are 

 dark lines or bands in the spectrum. The most striking and interesting of the 

 absorption spectra is the Solar Spectrum, or spectrum of sun-light. If this is ex- 

 amined carefully it will be found to be crossed by dark lines, the appearance be- 





