Descloizeaux, besides others by — svete; — with ar ea 
ions based thereupon res ertain mineral s tabulate 
the principal results as fur as thie sa ros cofffiiently done, svaulegin: ies facts 
si apa er the names of the species. 
4 table of Uniaxial species, the pone are (1) the Index of sibs on for 
the ecnary Pad (2) the same for ret pile aE ay; (8) the mean index of 
_Ttefrac stands for Bre r; Sen. for Senarmont; aid. for aidinger ; 
shel Heus, for len a = or Mile Rud. ‘for horn 
a in 
on, the maximum, n and minimum, ‘as afforded by three prisms,— 
xh ane 
F those giving the maximum and minimum, parallel ge techie 
2 Pictlvices of the ak and obtuse angles beeen n those axes. The thr 
ants of elasticity are consequently eek, to gmt c=. Aoamaecuale 
Y = 
e interior semi-angle of the optical axes about = axis of maximum elasti- 
diy, as Ric caca by means of the formula tana==? - = , he has compared with 
ee Al is “sete an from the mean index and the & appa me, angle measured 
sonal of a Wollaston goniomete r, using a tourmaline as an a analyzer and the hori- 
: mirr ores the goniometer as a po olarizer. He used in his investigations the 
cies, all the rhombohedral carbonates eed a I heed 
all the phosphates and arsenates are negative ; all the si 
ative. Levyne and phacolite are negative, but cnt fe is Ped 
tw ifferent varieties of apop! ; between 
between eudialyte and Penge Willemite (ete of zine ) is 
rate of esia are positive; oxyds of t nand zine are 
“epg ie ica is positive and anatase negative ; finally, 71 spéies are negative, 
byte, the Viaxial the carbonates of lime, bie be strontia, lead, are negative ; 
Tite ia ne negative but staurotide Repmeed! the most of the zevlites are positive i 
: nd stilbite afe e exceptions ot of baryta, strontia, lead, lime, anhy- 
drous are positive; tale an micas are negative ; clinochlore and ripid- 
are haan of the fiidaiats, orthoclase is negative, the others, viz. 
tbradorite, ano te and oligoclase are positive. Orthoclas e and the micas 
. — Pe a in the same specimen. In all, 70 species are positive, 
I, UNIAXIAL CRYSTALS. 
o2. 2 ees ceed arg axis the axis of least elasticity, 
1. 2. Extraord. _ 3, Mean Index. 
1: jaats 155828 (ray D) ; 
: 1562 
1-652 1°672 _(red ray) S. 
1667 728 
1961 2-015, Br. 
1°92 1:97, Sen. 
‘ 15431, Her. 
1569 1670 (red ray) Sen. 
| 1:3095 (yellow 
ray), Bravais. 
2 688 near ord., Mf. 
l 96 260 (red ray), Sen. 
Fifth Supplement to Dana’s Mineralogy. 397 
