SPHERICAL ELEMENTS OP CRYSTALS. 
205 
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balls (fig. 7.) One placed on the top of the three that are 
uppermost, forms the apex; and if the triangular ba»e on 
s^’hich it rests be enlarged by addition of three more balls regu- 
larly disposed around it, the entire group of ten balls will then 
be found to represent a regular tetrahedron. 
For the purpose of representing the acute rhomboid, two Tlie anite 
balls must be applied at opposite sides of the sma’lest octohe- 
dral group, as in fig. 9 . And if a greater number of balls be 
placed together, fig. 10 and 11 , in the same form, then a com- 
plete tetrahedral group may be removed from each extremity, 
leaving a central ortohedron, as may be seen in fig. 11 , which 
corresponds to fig. 3. 
Ihe passage of Dr. Hooke, from which I shall quote so 
much as to connect the sense, is to be found at page 85 of his 
Micrographia. 
" From this I shall proceed to a second considerable phc- Pass^e from 
nomenon, which these diamants (meaning thereby quartz <.ontainin)? * 
crystals) exhibit, and that is the regularity of their figure. theory. 
This I take to proceed from the most simple principle that any 
kind of form can come from, next the globular ; for — I think 
I could make probable, that all these regular figures arise only 
from three or four several positions or postures of globular 
particles, and those the most plain and obvious, and necessary 
conjunctions of such figured particles that are possible. And 
this I have adoculum demonstrated whli a company of bullets, 
BO that there was not any regular figure which I have hitherto 
met withal of any of those bodies that I have above named 
that I could not, with the composition of bullets or globules, 
imitate almost by shaking them together. 
" Thus, for instance, we find tliat globular bullets will, of 
themselves, if put on an inclining plane, so that they 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 is obvious, that a fourth globule laid upon the third in 
