104 Prof. Weiss on the Methodical and Natural Distribution 
my of Berlin, for 1814 and 1815, and which is entitled 46 Des 
Divisions Naturelles des Systemes de Cristallisation , par C. S. 
Weiss.” If there are some parts of this table which require 
correction, it is only in consequence of more recent discoveries, 
of which 1 could not then avail myself. 
In reading the memoir itself, you will find in it an explana- 
tion, that applies directly to the consideration of different axes, 
which ought especially to interest and direct the researches of 
the natural philosopher, of which you have given the most illus- 
trious proofs, in the discovery of the relation between the primi- 
tive forms of minerals, and the number of their axes of double 
refraction, a relation which does not appear to have been con- 
ceived or understood by M. Mohs. 
In another memoir, published in the subsequent volume of 
the Memoirs of the Academy of Berlin, for 1816 and 1817, I 
have explained my method of describing all the crystalline faces 
of any system whatever, in relation to the fundamental axes of 
the system, a method which I consider preferable to that of 
M. Mohs and I have also deduced from the polarisation of 
the latera of the crystalline axes, the most curious phenomena of 
crystallography, such as the reduction to one-half of a number of 
the co-ordinate faces, &c., a phenomenon which I have expressly 
described in my memoir of 1815, distinguishing always, in the 
same general division, those subdivisions which I have called 
Homoedriques (with the number of faces complete), and Hemie- 
driques (with the number of faces reduced to one-half). I have 
besides pointed out the application of my crystallographic me- 
thod, to the developement of some particular systems of a diffi- 
cult nature, such as those of Feldspar and Epidote, which were 
considered so by Hatiy. I might also mention other memoirs, 
. which I have published among those of the Academy of Berlin 
for 181 8, 1819, either on the mathematical theory of crystallo* 
nomy, or on topics particularly interesting to natural philoso- 
phers ; such as the comparison which I have made between the 
geometrical relations of the dimensions of the principal solids of 
a regular system, and those of the harmonic intervals in music. 
Unluckily, however, none of these memoirs have been more for- 
tunate than the first with M. Mohs, to whom I sent them as 
soon as they were printed, excepting that of 1815, when M. 
