412 Method of expreffing the Forms of Cryftals. 
. 6, Every whole number, placed towards the top and on 
the right or ‘left of a letter, denotes. a decrement which 
takes place to the right or left of the angle, or of the eet 
marked with the fame letter. 
4. Every letter, fuch as 3H” or G, which ‘ bears fevevall 
figures, placed different ways or in the fame manner, indi- 
cates that the correfponding edge or angle undergoes, at the 
fame time, different kinds of decrements musa by 
the numbers. 
8. The fraétions 4, 4, 4, &c. which have unity for nume- 
rator, denote decrements in height by two, three, four 
ranges, &c. 
g. The fraétions 3, 3, 3, &c. each term of which is 
greater than unity, denote mixed decrements by two ranges 
in breadth and three in height, or by three ranges in 
breadth and four in hoght, or by three in breadth and twe 
in height. 
10, The parenthefis, fuch as O D" F*), denotes an inter- 
mediary decrement. The letter O indicates: firft that the 
decrement takes place by three ranges on the angle O, and 
that its effect is afcending. D* F* make known that for 
one edge of molecule fubtraéted along the fide marked D, 
there are two edges fubtra¢ted along the fide marked F. 
11. Every fmall letter, comprehended in the fign of a 
cryftal, indicates the angle or edge diametrically oppofite to 
that which bears the large letter of the fame name on the 
figure; or the fmall letter in queftion is omitted as fuper- 
fluous. 
12. We mutt except the letter e, which is always found 
on the figure of the rhomboid, and which indicates the 
angle oppofite to that which bears the letter E. 
13. When a fign contains two letters of the fame name, 
one large and the other fmall, with different figures, the 
two angles or two edges oppofite to which thefe letters. cor- 
-refpond, are fuppofed to undergo each feparately the law of 
decrement indicated by the figure that accompanies it, 
14. Every 
