the different Cryfialline Forms. 41 
which: may ferve to give a’clear idea of it, and enable san 
obferver to reprefent immediately a fecondary cryfial of 'a 
given form. But if any one fhould confine himfelf merely 
‘to a knowledge of the figns employed in this method, and 
fhould only with to read them, without being defirous to 
know the art of writing them, a few fimple rules only will 
be neceffary to be known, which I fhall here briefly men- 
tion; they will form a review of the preceding details. 
1. Every vowel employed in the fign of a cryftal denotes 
the folid angle, marked with the fame yowel on the figure 
reprefenting the nucleus; and every confonant indicates 
the edge which bears that confonant, or the face, the middle 
pf which it-occupies on the figure of the nucleus. 
2. Each yowel and each od etd is accompanied with 
one or more figures ; the values of which, as well as the 
pofitions, satiate the laws of decrement which the angles 
or correfponding edges undergo. We mutt except the three 
confonants P, M, T, each of which, when it forms part of 
the fi ign of a cryftal, indicates that the cryftal has faces 
arallel to that which bears this letter. 
3. Each letter, comprehended in the fin of a cryftal, is 
underftood, with the cipher or ciphers that accompany it, 
on all the aneles or edges, which perform the fame functions 
as that which, in the figure, is immediately marked with 
the letter in queftion. 
4. Every whole number, placed above.a letter; indicates a 
decrement 1 in breadth, which afcends in departing from the 
pale or edge marked with that letter. 
- 5. Every whole number, placed below a letter, indicates 
a decrement which defcends in departing cither from the 
funimit or the edge which bears that letéer *, 
* Allufion is made here to the general progrefs of decrements, to-which 
the particular cafes that feem to make an exception are referred. For 
example, if the decrement took place by one range on the angle at the fum- 
mit of a rhomboid, the face produced would be horizontal; but this decre- 
ment enters into thofe which are defcending, and of which it is, as it 
were, the boundary. 
6. Every 
