150 MICRO-SPECTROSCOPE AND POLARISCOPE [CH. VI 



what enables us to do so with certainty is the fact : that the two solu- 

 tions give bands of equal intensities in the same parts of the spectrum 

 which undergo analogous changes on the addition of the same reagent. ' ' 



REFERENCES TO THE MICRO-SPECTROSCOPE AND 

 SPECTRUM ANALYSIS 



The micro-spectroscope is playing an ever-increasingly important role in the 

 spectrum analysis of animal and vegetable pigments, and of colored mineral and 

 chemical substances, therefore a somewhat extended reference to literature will be 

 given. Full titles of the books and periodicals will be found in the Bibliography 

 at the end. 



Angstrom, Recherches sur le spectre solaire, etc. Also various papers in 

 periodicals. See Royal Soc's Cat'l Scientific Papers ; Anthony & Brackett ; Beale, 

 p. 269 ; Behrens, p. 139 ; Kossel und Schiefferdecker, p. 63 ; Carpenter, p. 323 ; 

 Browning, How to Work with the Spectroscope, and in Monthly Micr. Jour., II, 

 p. 65 ; Daniell, Principles of Physics. The general principles of spectrum analysis 

 are especially well stated in this work, pp. 435-455 ; Davis, p. 342 ; Dippel, p. 

 277 ; Frey ; Gamgee, p. 91 ; Halliburton ; Hogg, p. 122 ; also in Monthly Micr. 

 Jour., Vol. II, on colors of flowers; Jour, Roy. Micr. Soc., 1880, 1883, and in 

 various other vols. ; Kraus ; Lockyer ; M'Kendrick ; MacMunn ; and also in 

 Philos, Trans. R. S., 1886; various vols. of Jour. Physiol.; Nageli und Schwend- 

 ener ; Proctor; Ref. Hand-Book Med. Science, Vol. I, p. 577, VI, p. 516, VII, p. 

 426; Roscoe ; Schellen ; Sorby, in Beale, p. 269; also Proc. R. S., 1874, p. 31, 

 1867, p. 433 ; see also in the Scientific Review, Vol. V, p. 66, Vol. II, p. 419. 

 The larger works on Physiology, Chemistry and Physics may also be consulted 

 with profit. 



Vogel, Spectrum analysis ; also in Nature, Vol. xix, p. 495, on absorption spec- 

 tra. The bibliography in MacMunn is excellent and extended. 



For hemochromogen in medico-legal cases see Bleile, Trans. Amer. Micr. 

 Soc., 1900, p. 9. 



MICRO-POLARISCOPB 



g 218. The micro-polariscope, or polarizer, is a polariscope used in connection 

 with a microscope. 



The most common and typical form consists of two Nicol prisms, that is, two 

 somewhat elongated rhombs of Iceland spar cut diagonally and cemented together 

 with Canada balsam. These Nicol prisms are then mounted in such a way that 

 the light passes through them lengthwise, and in passing is divided into two rays 

 of plane polarized light. The one of these rays obeying most nearly the ordinary 

 law of refraction is called the ordinary ray, the one departing farthest from the 

 law is called the extra-ordinary ray. These two rays are not only polarized, but 

 polarized in planes almost exactly at right angles to each other. The Nicol prism 

 totally reflects the ordinary ray at the cemented surface as it meets that surface at 

 an angle greater than the critical angle, and only the extraordinary or less refracted 

 ray is transmitted. 



