die, and Contracting gradually at each end; black, fmooth, fliining
'ds glafs.
■ -Fig- A very large grain of tin ; the prifmatic ridges in which
this metal delights, are here placed nearly at right angles. It has
a fmall rhomboid plane at the point of infertion where the ridges
meet at e ; but where the fides of the two ridges fhould meet, as
at f f> the7 are tJ:iere planed oif. Thelargeft tin-grain I have’ yet
iSTeen.’
wtyq^a»®!lie furface of this grain is divided into -eight .triangular
pknds, fe applied to one' another iks\ to, conftitute four ridges meeting
in a fmall central Thisfigure is"very rare, and the planes
o f a high polifh.
; vnr. ^A columnar grain on rhdmboidal bafe.
ix. D°. mote diftind:," the apex a quadrilateral pyramid.
x. A 'bunch -of tin-grains, conne&ed as if one large “ grain with
its furface differ’erftf^fhot. <The figures are pyramidal and cuneoid,
sthree'^f. the lattef fpread like the toes o f a bud from the point of
1 contad.
'§ xi. -An ^equilateral' triangular plane :,pfojeding.! from atparallel
edged on' one fide with a quarter-rdund bead parallel to the
aajdining| fide - ofithe triangle.
1 , • ' pyramidal pentahedral grain perfectly: fmooth and\black;
its front cdiififts of 'two unequal equilateral triangles, divided by a
{ulcus j o f the other TaCes of the pyramid, two are, cuneoid, the
other circular.
xin. Plan of the foregoing pyramid, N°. xii.
xivri A quadrilateral, irregularly-pyramidal grain. The two
'ends are cuneoid, the1 two fides defcend from thqs ’apex in a Hope,
ftriat^tl-to the bottom, where the Jlruz fpread off in an obtufc an-
ffidefighed tofbrm another pyramidal procefs o f like ftruc-
•%tre on' each fide.
- xv. Another o f like form, but more finifhed in figure, and of
a higher polifh. -
xvi. A plan of' a quadrangular pyramid on a column of a nearly
fquare bafe; one face of the pyramid is divided into , two nearly
equal triangles by a fubfidence in the middle, approaching fbme-
what to N\ vii.
xvffv The elevation of NVx vi.
xv lift Grain-tin melted, firft in the common way, then farther
purified, as far as the prefent method will permit.
•• xix. A, the front,' and B (by fcale annexed) the back-view of
an ancient block of tin, explained before, page 163. ;
XX. A curious grain of tin, black and Aiming, with flammulec of
a golden colour 5 the feces pentahedral; but the greateft rarity of this
fpecimen