SPHERICAL ELEMENTS OF CRYSTALS. 
ail 
that with a certain degree of softness, and of relative attrac* 
tion, the particles will be surrounded each by four others, and 
will all be tetrahedral, although, in fact, it be demonstrably 
impossible that tetrahedrons alone should fill any space. 
It is next supposed, that soft spheres less compressed will Objections, 
be surrounded by five others, and will be formed into triangular 
prisms, comprised under five similar and equal planes. That 
they should be similar is impossible, and it is further demon- 
strable, that when the triangular termination of such a prism 
is equal in area to each rectangular side of the prism, so as to 
present equal resistance, according to the hypothesis, then the 
triangular faces will be nearer to the centre in the proportion 
of three to four, so that the attractions will not be equal as the 
hypothesis would require. 
A third hypothesis of M. Prechtl is, that the degree of com- 
pressibility may be such that each particle will be surrounded 
by six others, giving it the form of a cube, which, it must be 
admitted, is a very possible supposition. 
All further application of the same hypothesis is precluded 
by M. Prechtl, by denying that one particle can be surrounded 
by more than six others j' although, in fact, it is most evident, 
that any sphere, when not compressed, will be surrounded by 
twice that number, and consequently by a slight degree of 
compression will be converted into a dodecahedron, according 
to the most probable hypothesis of simple compression. 
y^nnotalion.-^-W . N. 
Dr. George Fordyce, at the end of his pamphlet entitled 
“ Elements of Agriculture and Vegetation," published in 
I.,ondon, 1771, has given three plates to show the combination 
of bodies by the apposition of the spheres which surround the 
particles where the powers of attraction and repulsion are in 
equilibrio. He considers the chemical union of two particles 
as producing a compound endued with a new sphere of action ; 
as. 
