192 SEVENTH REPORT—1837. 
and yet if the optical property is to be depended upon, the ar- 
rangement of the molecules in the natural juice must have dif- 
fered very materially from their arrangement in the artificial 
solution. Unfortunately we cannot depend on the purity of 
the natural juice, and therefore it would be premature to draw 
from this phenomenon any of those curious consequences in 
regard to the value of optical characters and the possibility of 
the dimorphous molecular arrangement of a solid body follow- 
ing it into its state of solution—which the absolute chemical 
purity of the sugar in the natural and artificial liquids would 
render justifiable. 
W. 
38. Of crystallized bodies not known to assume more than 
one form, which yet exhibit unlike physical properties in dif- 
ferent portions of their mass.—There are certain mineral sub- 
stances, the crystalline form and chemical constitution of which 
are known and constant, which nevertheless in their action on 
light exhibit phenomena apparently inconsistent with the idea 
that the several parts have the form and composition of the 
whole. As these phenomena are closely related to those of 
dimorphism, and may possibly be identical with them, I shall 
here introduce a notice of the more remarkable cases in which 
they occur. The greater number of these observations have been 
made and published by Sir David Brewster. 
Apophyllite—In a paper published in the Edinburgh Phil. 
Trans., vol. ix. p. 317, Sir David has shown that the crystals 
of certain varieties of apophyllite consist of different portions 
acting differently on light: ‘* An individual crystal, with one 
axis, being symmetrically united with several individual crystals 
with two axes, so as to constitute a regular crystal.” Ina 
single fragment of a crystal of this substance Sir John Herschel 
also found three portions, each possessing distinct and pecu- 
liar properties.—Whewell’s Report on Mineralogy, p. 353. In 
the amethyst he has described an analogous structure. 
Analcime.—This mineral occurs usually in icositetrahedrons, 
made up of twenty-four individual pentahedrons. These penta- 
hedrons exhibit “‘ a species of double refraction, previously 
found in no other mineral.” They possess “ planes of no 
double refraction, having a definite and invariable position, and 
a portion may be extracted from each separate pentahedron 
which has no axis at all.’’* 
Chabasie——Some specimens of this well-known mineral, 
when examined by polarized light, appear to consist of success- 
* Edinburgh Philosophical Transactions, 1824. 
