180 On the Humite of Monte Somma. 
Poe in the lettering, as explained in the last volume of this 
a the crystals, the symbols of the planes may be at once 
read off, and those of each series compared. There is a remark- 
‘able simplicity in the series ;—and moreover, the parallelism 
between these related forms is well brought out; we appear 
maserat to be sustained in this mode of viewing these complex 
c 
We observe that— 
The m:1: & seriesin fig. A, (¢ of Scacchi), ee $,3,3,3,2 
The “ “« in fig. B, ii %, $s Bit 
The “ « infig.C, soiiengs ea 
Them:1:1 “ (rabove) in fig. A, has for m the values $,2,3,.3 1% 
The « « in fig, B, < ss 2,32 
The “« “ in fig. C, - 2 4, 4, boi $a is 
The m: & : 1 series (i above) in fig <pcqpale ng 2 3,2, & 
“as nigh * } 
‘his ta “ aR: «aoe 6 
2) t 
The values of m for the series m: 1:2, (n above) na for m:1:3, 
(m above) will be read off from the figure. 
In this method therefore, we have no sacrifice of accuracy in 
the angles, nor of simplicity in the exhibited ‘relations of the 
planes; on the contrary, the crystals are more readily compar 
and their actual differences more easily noted, than by Scacchi’s 
method. 
We gather at once, that the three crystals although approxi- 
mately alike in their vertical axes, differ in the igeateze ical series 
expressing the positions of the secondary plan 
th series are— 
or fig, B, 2, 3 ihe £, 2, or 3, 3,8, %, the latter not essentially differ- 
ing he the. for as the two are alike in the alternate terms. 
For fig. B, 2, he 22. 
For fig. C; $4, 4, $5 $s tr vr 
writer has thought it preferable to use the letter I (or , for o (infinity) 
instead ‘of O (or 0), (as proposed in volume rib page 399), since the letter O is 8 
readily co place Nau- 
confounded with 0 (zero). B plana ; this 
mann’s crystallographic fymbols sixbaapeading ‘ or ot Gane oF of 
Fg4$ 2 3 1 Dt HH H 1 sx a HO & 
Naum, §P ?P 3P <P %,Pn BPH 2Pa Po Pe 8Py 2Po afs aPo 
% In writing the symbols, wch a 32, the writer proposes to put in a hyphen, 
thus, 1-2, 3-2; on the crystal thi rarely necessary. 
In the above re i wan fo 8 in nd to make ‘more obvious the relations of 
t The plane of composition fr twins of fig, II or B and not an observed plane. 
Ae + hag 
