hy Doiihly Refracting Crystals. 345 
The following table shows the characters of the tints in cry- 
stals with two axes, which have not been examined in every azi- 
muth. 
Mica 
Acetate of copper 
Muriate of copper ^ 
Olivine 
Sphene 
Nitrate of copper 
Chromate of lead 
Staurotide 
Augite 
Anhydrite 
Axinite 
Diallage 
Sulphur 
Sulphate of strontites 
— cobalt 
Olivine 
Axis of prism in the 
plane of primitive po- 
larisation. 
Blood red 
Blue 
Greenish white 
Bluish green 
Yellow 
Bluish white 
Orange 
Brownish red 
Blood red 
Bright pink 
Reddish white 
Brownish white 
Yellow 
Blue 
Pink 
Brown 
Axis of prism perpendicu- 
lar to the plane of pri- 
mitive polarisation. 
Pale greenish yellow 
Greenish yellow 
Blue * 
Greenish yellow 
Bluish 
Blue 
Blood red 
Yellowish white 
Bright green 
Pale yellow 
Yellowish white 
White 
Deeper yellow 
Bluish white 
Brick red 
Brownish white 
In the last eight crystals of the preceding table, the tints are 
not given in relation to any fixed line, 
The following table contains the characters of the two pen- 
cils in crystals, the number of whose axes 1 have mot yet deter- 
mined. - 
Phosphate of iron 
Actinolite 
Precious opal 
Serpentine 
Asbestos 
Blue carb. of copper 
Octohedrite ( one axis ) 
Fine blue t 
Green 
Yellow 
Dark green 
Greenish 
Violet blue 
Whitish brown 
Bluish white 
Greenish white 
Lighter yellow 
Lighter green 
Yellowish 
Greenish blue 
Yellowish brown 
Several of the preceding crystals which have a laminated 
structure, such as mica, epidote, &c. or such as have an imper- 
fect transparency from a defective aggregation of their elemen- 
tary crystals, frequently exhibit their absorptive qualities, and 
also their system of coloured rings, by exposure to common 
light. The light is, in these cases, analysed in passing oblique- 
* The tint's are given in relation to the short diagonal of its rhomboidal base. 
When the axis of the prism vi'as in the plane of primitive polarisation. 
VOL. II. NO. 4. APRIL 18S0. 
Z 
