SPHERICAL EI.ExMENTS OF CRYSTALS. 
203 
contact of adjacent particles is only at their edges ; and 
although in such an arrangement it must be admitted that there 
may be an equilibrium, it is evidently unstable, and ill-adapted 
to form the basis of any permanent crystal. 
More than three years have now elapsed since a very simple Explanation 
explanation of this difficulty occurred to me. As in the course 
Uifiirnltj isob- 
of that time I had not discovered it to be liable to any crys- 
tallographical objection, and as it had appeared satisfactory to 
various mathematical and philosophical friends to whom I pro- 
posed it, I had engaged to make this the subject of the 
Bakerian lecture of the present year, hoping that some fuither 
speculations, connected with the same theory, might lead to 
more correct notions than are at present entertained of crys- 
tallization in general. 
At the time when I made this engagement, I flattered my- 
self that the conception might be deserving of attention from dently cli^co- 
its novelty. But I have since found, that it is not ali< gether Hooke.*'^ 
so new as I had then supposed it to be ; for, by the kindness of 
a friend, I have been referred to Ur. Hooke’s Micrographia, 
nn which is contained, most clearly, one tjssential part of the 
■same theory. 
However, since the office of a lecturer is properly to diffuse 
dvnowledge already acquired, rather than to make known new 
discoveries in science, and since these hints of Dr. Hooke have 
bbeen totally overlooked, from having been thrown out at a 
[time when crystallography, as a branch of science, was wholly 
I unknown, and consequently not applied by him to the extent 
■which they may now admit, I have no hesitation in treating 
ilhe subject as I had before designed. And when I have so 
done, I shall quote the passage from Dr. Hooke, to shew how 
rixactly the views which 1 have taken have, to a ce tain extent, 
c.:orrespondcd with his ; and I shall hope that, by the assistance 
of such authority, they may meet with a more favourable recep- 
ttion. 
The theory to which I here allude is this — that, with respect T to theory, 
tco fluor spar, and such other substances, as assume the octohe- f ctli syiu n-' 
dral and tetrahedral forms, all difficulty is removed by suppos- ““d 
ing 
