~ M. C. Lea on Optical Properties of Picrate of Manganese. 403 
the one hand, or the manganese and cadmium or the other, are 
prismatically elongated in the direction of a secondary axis. — 
It is convenient that distinct phenomena should have distinct 
names, and none appears to have been assigned to ween Brews- 
ter speaks of it as a ‘property of light,” and Haidinger uses 
the word “Schiller” forit. ‘The terms dichroism, trichroism and 
flect, (as a polished surface,) applying it to ex- 
Gites the ehiperey at anti ee two beams, one normally polar- 
ized in the plane of incidence and the other polarized in a plane 
perpendicular to it. 
i rties exhibited by the picrates of ammo- 
hg vs | pouall revel? remarkable in their variety. Their 
eryst hist sabi 
“ist The wel known play of red and green light. If a little 
very dilute solution of pure picrate of potash be spontaneously 
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