64 On the elemeniary Particles of cerluin Crystals. 
hedron; so that asixth ball similarly placed underneath 
the square will complete the octohedral group, fig. 6. 
There is one observation with regard to these torms that’ 
will appear paradoxical, namely, that a structure which In 
this case was begun upon a square foundation, is really in- 
trinsically the same as that which is begun upon the tri- 
angular basis. But if we lay the octohedral group, which 
consists of six balls, on one of its wiangniar sides, and 
consequently with an opposite triangular face uppermost, 
the two groups, consisting of three balls each, are then 
situated precisely as they would be found in two adjacent 
strata of the triangular arranzement. Hence in this posi- 
tion we may readily convert the octohedron into a regular 
tetrahedron, by addition of four more balls. (fig. 7.) One 
placed on the top of the three that are uppermost forms the 
apex; and if the triangular base, on which it rests, be en« 
larged by addition of three more balls regularly 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 
balls must be applied at opposite sides of the smallest octo- 
hedral group, as in fig. g. And if a greater number of 
balls be placed together, fig. 10 and 11, in the same form, 
then a complete tetrahedral group may be removed from 
each extremity, leaving a central octohedron, as may be 
seen in fig. 11, which corresponds to fig. 3. 
The 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 Micrograr bia. 
“ From this I shall proceed to a second considerable 
phenomenon, which these diamants (meaning thereby 
quartz crvstals) exhibit, and that is the regularity of their 
figure This 1 take to proceed from the most simple 
principle that any kind of form can come from, next the 
globular ;_ tor I chink | 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 
ad oculum demonstrated with a company of bullets, so that 
there was not any regular figure which ! have hitherto met 
withal of any of those bodies that | 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. that globular bullets will 
of themselves, if put on an inclining plain so that they 
may 
