410 . Short Method of expreffing » 
trations of one range ou the fix edges D, D, &c.5 and the 
other three by fubtractions of two. ranges on three only of 
the, angles E or e..» Moreover, the inferior fummit’ has 
fimply three faces parallel to thofe of the nucleus; while on 
the fuperior fummit the three edges B are each, replaced by 
a facet, in confequence of a decrement by one range which 
does not attain to its limits. The reprefentative fign of this 
form will be: De EPB, b. The quantities , b fhew, 
the firft that the angles oppofite to e undergo no decrement, 
and the other that the edges oppofite to B remain alfo un- 
touched. If thefe edges were fubjected to a different 
law, taking place by two ranges, the fign would become 
De EP B . According to this we are fuppofed to admit 
that the decrements, reprefented by a large letter, do not 
"implicitly contain like decrements analogous to the. fmall 
letter of the fame name; or reciprocally, that if the fecond 
letter fhould not enter into the expreffion of the fign with a 
different figure, we fhould not place there the fame figure 
accompanied with a zero, In the firft cafe, each of the 
two letters expreffes a decrement which is peculiar to the 
edges or angles it denotes; in the fecond, that which is 
affected by a zero fhews that the angle or edge it denotes 
undergoes no decrement, ; 
38. Let us ftill quote the variety cf the fulphure of zinc, 
which exhibits the dodecaedron having rhombufes for its 
planes, the four folid angles of which, campofed of three 
planes, are replaced by triangular facets fituated like the 
faces of a tetraedron, while the oppofite angles remain ung 
touched *, By always adopting figure 16 to reprefent the 
primitive form, we fhould thus exprefs the variety in quel- 
I. 
tion : A a A 7 
39s "T. bare enlarged upon the explanation of the princi- 
ples of this method, that I might, if poffible, omit nothing 
* This variety*is fill modified by Osher facets, of which, for the greater 
fimplicity, no actice is keg. 
which 
