CH. VI.~\ MICRO-SPECTROSCOPE AND POLAR/SCOPE. 139 



the polarizer and the object. If properly mounted, the selenite is very 

 conveniently placed on the diaphragm carrier of the Abbe illuminator, 

 just above the polarizer. A thin plate or film of mica also answers well. 



It is not necessary to use a selenite or piece of mica for the produc- 

 tion of the most glorious colors in many objects. One of the most 

 beautiful preparations, and one of the most instructive also, may be 

 prepared as follows : Heat some xylene balsam on a slide until the 

 xylene is nearly evaporated. Add some crystals of the hypnotic medi- 

 cine, sulphonal and warm till the sulphonal is melted and mixes with 

 the balsam. While the balsam is still melted put on a cover-glass. If 

 one gets perfect crystals there will be shown not only most beautiful 

 colors, but the black cross with perfection. (Clark). 



It is very instructive and interesting to examine organic and inor- 

 ganic substances with a micro-polarizer. If the objects enumerated in 

 § 144 were all examined with polarized light an additional means of de- 

 tecting them would be found. 



REFERENCES TO THE POEARISCOPE AND TO THE USE OF POLARIZED 



LIGHT. 



Anthony & Brackett ; Bebrens, 133 ; Behrens, Kossel uud Schiefferdecker ; Car- 

 ney, 61 ; Carpenter-Dallinger, 262, 269, 992 ; Clark ; Daniell, 494 ; Davis ; v. Ebe- 

 ner ; Gage ; Gamgee ; Halliburton, 36, 272 ; Hogg, 133, 729 ; Lehmann ; M'Ken- 

 drick ; Nageli und Schwendener, 299; Queckett ; Suffolk, 125; Valentin. Physi- 

 cal Review, I., p. 127. Daniell, Physics for Medical Students. 



