_Scheme_. If a fourth be
joyn'd to them on either side as closely as it can, they four compose the
most regular Rhombus consisting of two _aequilateral triangles_, as B. If a
fifth be joyn'd to them on either side in as close a position as it can,
which is the propriety of the _Texture_, it makes a _Trapezium_, or
four-sided Figure, two of whole angles are 120. and two 60. degrees, as C.
If a sixth be added, as before, either it makes an _aequilateral triangle_,
as D, or a Rhomboeid, as E, or an _Hex-angular Figure_, as F, which is
compos'd of two _primary Rhombes_. If a seventh be added, it makes either
an _aequilatero-hexagonal_ Figure, as G, or some kind of six-sided
_Figure_, as H, or I. And though there be never so many placed together,
they may be rang'd into some of these lately mentioned Figures, all the
angles of which will be either _60_. degrees, or 120. as the figure K.
which is an _aequiangular hexagonal_ Figure is compounded of 12.
_Globules_, or may be of 25, or 27, or 36, or 42, &c. and by these kinds of
texture, or position of globular bodies, may you find out all the variety
of regular shapes, into which the smooth surfaces of _Alum_ are form'd, as
upon examination any one may easily find; nor does it hold only in
superficies, but in solidity also, for it's obvious that a fourth _Globule_
laid upon the third in this texture, composes a regular _Tetrahedron_,
which is a very usual Figure of the _Crystals_ of _Alum_.
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