504 • APPENDIX. 



property of polarizing light, with a power superior to that of 

 the tourmaline. 



By careful manipulation, crystals have been obtained by the 

 discoverer. Dr. Herapath, of Bristol, sufficiently large and 

 transparent to be used as a polarizer, and have been adapted 

 by him to the field of the microscope ; all the usual pheno- 

 mena of the polarizing microscope can be exhibited by means 

 of this chemical combination of iodine and disulphate of 

 quinine. When these crystals are examined by two Nicols' 

 prisms or two tourmahnes, it is also evident that at certain 

 angles of rotation they possess the power of depolarizing light, 

 and thus conduct themselves as a plate of selenite would do 

 under the same circumstances. 



