364 1. Dr. Brewster’s Memoirs. 
moved by correcting the primitive forms of the minerals 
which then stood as exceptions, 
The present paper is principally occupied by a compar- 
‘ison of Haity’s Primitive forms with the fundamental forms 
of Mohs and the Optical System of Dr. Brewster. 
The following Table will exhibit the results of this com- 
parison. ; cry 
al Forms. cal System. 
Haiiy’s Primitive ; Mohs’ Fundamen- Brewster’s Opti- 
~ Forms. tal F S 
Rhomboid 
Reg. Hexahed. 
iste homboidalSystem | Crystals wet 
rism 
Bipyramid. Dode- NE’ AXIS 0 
‘ a Double Refrac- 
ctohedron ? Base Wie y: tion. 
Right Prism square Fyramidal System 
Right Prism—Base : 
not square | Crystals with 
Oblique Prism —___ Prismatic System J two axes of 
Octohedron-Base . Double Refrac- 
a rectangle tion. 
or rhomb. 
Crystals with THREE 
Cube ) rectangular axes 10 
Reg. Octohedron \ Tessular Sys- } a state of equilib- 
Rhomb. Dodeca- ? tem . rium and therefore 
hed. producing no Doub 
: le Refraction. 
* 
ted with great delicacy, and are all referable to the red, 
o specimens 
which exhibited the green rays. The crystals in almost 
all Dr. B’s specimens are tesselated in a peculiar manners 
not / rope or turned half way round or any determinate 
portion of a circle, but polytrope, the principal sections # 
~ 
