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Proceedings of the Boyal Society 
carry on my correspondence with them in this indirect manner, for 
which I beg you will make my apology. Kemember me also to all 
my friends in Edinr., — to whom I consider myself as writing when 
I address my letters to you. Best eompts. to Mrs Alison, &c. &c. — 
I ever am, dear Archy, yours sincerely. 
July 2.” 
“ D. S. 
2. The Law of Aeriform Volumes extended to dense bodies. 
By J. G. Macvicar, A.M., D.D. Communicated by Pro- 
fessor Lyon Playfair. 
In this communication the author proceeds to show that when 
dense bodies, whether liquids or solids, are regarded as consisting 
of certain molecules, the volumes of these molecules are either 
equals, halves, or doubles, &c., as in aeriforms. 
This he proves by showing that the densities of bodies in gene- 
ral, as determined by the balance, are proportional to the numbers 
which express the weights of their molecules. 
The author’s theory of molecules is based on the following reason- 
ing. By the general consent of men of science, nature is a dyna- 
mical system — a system of applied mathematics. The molecules 
of bodies are, when compared with the other properties of bodies, 
very stable clusters of atoms. In their structure, therefore, they 
may be expected to display in a high degree the geometrical and 
the dynamical, that is, the mechanical conditions of stability. 
These conditions in reference to individualised objects, each hav- 
ing but one centre, that is, in reference to such structures as the 
molecules of bodies, are most perfectly fulfilled, when the group 
of their parts or particles, regarded geometrically, is reducible to 
one or other of the regular polyhedrons. These polyhedrons are 
five in number ; and of these, three (the tetrahedron, octohedron, 
and icosahedron) are of the same order, all having triangular faces ; 
and all the three may be regarded as culminating in the last named 
and most perfect of the three, viz., the isocahedron. But the 
icosahedron, in its turn, is most intimately related to the dode- 
cahedron, each under the application of the law of symmetry 
