which serve for the two species of refraction; and when meeting the
second crystal in another position are able to move only one of these
kinds of matter. But to tell how this occurs, I have hitherto found
nothing which satisfies me.
Leaving then to others this research, I pass to what I have to say
touching the cause of the extraordinary figure of this crystal, and
why it cleaves easily in three different senses, parallel to any one
of its surfaces.
There are many bodies, vegetable, mineral, and congealed salts, which
are formed with certain regular angles and figures. Thus among flowers
there are many which have their leaves disposed in ordered polygons,
to the number of 3, 4, 5, or 6 sides, but not more. This well deserves
to be investigated, both as to the polygonal figure, and as to why it
does not exceed the number 6.
Rock Crystal grows ordinarily in hexagonal bars, and diamonds are
found which occur with a square point and polished surfaces. There is
a species of small flat stones, piled up directly upon one another,
which are all of pentagonal figure with rounded angles, and the sides
a little folded inwards. The grains of gray salt which are formed from
sea water affect the figure, or at least the angle, of the cube; and
in the congelations of other salts, and in that of sugar, there are
found other solid angles with perfectly flat faces. Small snowflakes
almost always fall in little stars with 6 points, and sometimes in
hexagons with straight sides. And I have often observed, in water
which is beginning to freeze, a kind of flat and thin foliage of ice,
the middle ray of which throws out branches inclined at an angle of 60
degrees. All these things are worthy of being carefully investigated
to ascertain how and by what artifice nature there operates. But it is
not now my intention to treat fully of this matter. It seems that in
general the regularity which occurs in these productions comes from
the arrangement of the small invisible equal particles of which they
are composed. And, coming to our Iceland Crystal, I say that if there
were a pyramid such as ABCD, composed of small rounded corpuscles, not
spherical but flattened spheroids, such as would be made by the
rotation of the ellipse GH around its lesser diameter EF (of which the
ratio to the greater diameter is very nearly that of 1 to the square
root of 8)--I say that then the solid angle of the point D would be
72