434 Mr. WHEWELL on the Selection of a Notation 
(R + 2)°, (R—3)*, &e. 
these .R, _3R,, &c. which agree very nearly with 
2R3 2-*R2, &c. the symbols here proposed. 
6. A rule is given, Mohs, Sect. 96, to refer the members of 
the subordinate series to the members of the principal series, 
whose axis comes nearest to them. This rule introduces com- 
plicated expressions unnecessarily, because the subordinate form 
may have a very complicated ratio to the nearest principal form, 
though a very simple one to some other. Thus, we have a form 
in the square-pyramidal system, which is represented by 
—— P-3; 
3 
its axis being, therefore, 
Hence, if we refer it to P, the fundamental form of it will be 
+P. By this mode of designating the forms (particularly in 
the square-pyramidal system), we lose sight of the simplicity of 
the law by which they are deduced. 
7. In the same manner in which Mohs changes R into P, 
when the rhombohedron becomes a pyramid, he changes, in the 
pyramidal system, P into Pr, when the pyramid becomes a prism. 
Here, however, some alteration is necessary, because the indices, 
in this case, become infinite, and, therefore, the symbol incon- 
venient. I have adopted, in some measure, this part of the no- 
tation, but with these advantages, that the r added indicates, in 
our method, a particular process, the analogy of which runs 
through all the systems; and, also, that the letter P, which 
recurs in the symbol, marks the fundamental form from which 
the deduction is made. 
