On the elementaty Particles of certain Crystals. 65 
May run together, naturally run into a triangular order 
composing all the variety of figures that can be imagined 
out of equilateral triangles, and such you will find upon 
trial all the surfaces of alum to be composed of 
*€ nor does it hold only in superficies, but in solidity 
also; for it’s obvious that a fourth globule jaid upon the 
third in this texture composes 4 regular tetrahedron, which 
is a very usual figure of the crystals of aium. And there is 
no one figure into which alum is observed to be crystallized, 
‘but may by this texture of globules be imitated, and by no 
-otber.” 
It does not appear in what manner this thost ingenious 
philosopher thought of applying this doctrine to the forma- 
tion of quartz crystal, of vitriol, of salt-petre, &c. which 
he names. This remains among the many hints which the 
peculiar jealousy of his temper left unintelligible at the time 
they were written, and which, notwithstanding his inde- 
fatigable industry, were subsequently lost to the public, for 
want of being fully developed. | 
We have seen, that by due application of spheres to each 
other, all the most simple forms of one species of crystal 
will be produced, and it is needless to pursue any other 
modifications of the same form, which must result from a 
series of decrements produced according to known laws. 
Since then the simplest arrangement of the most simple 
solid that can be imagined, affords so complete a solution 
of one of the most difficult questions in crystallography, 
we are naturally led to inquire what forms would probably 
occur from the union of other solids most nearly allied to 
the sphere. And it will appear that by the supposition of 
elementary ‘particles that are spheroidical, we may frame 
conjectures as to the origin of other angular solids well 
known to crystallographers. 
The oltuse Rhomboid. 
If we suppose the axis of our elementary spheroid to be 
its shortest dimension, a class of solids will be tormed which 
are numerous in crystallography. {[t has been remarked 
above, that by the natural grouping of spherical particles, 
fig. 10, one resulting solid is an acute rhomboid, similar to 
that of fig. 2, having certain determinate anyles, and its 
greatest dimension in the direction of its axis. Now, if 
other particles having the same relative atrangement be 
supposed to have the form of oblate spheroids, the resulting 
solid, fig. 12, will still be a regular rhomboid; but the 
measures of its angles will be different from those of the 
Vol. 42, No. 183, July 1813. E former, 
