DE. A. W. HOFMAIfN ON THE PHOSPHOEUS-BASES. 
613 
According to Naumann : — • 
= 0-9945: 1:1-0013; y = 86° 52'. 
Forms observed: — ■ 
OO P 00, OP, oo P, P oo. 
According to Weiss : — 
a:b:c = l: 1-0013 : 0-9945 ; aoc"9S° 8'. 
Forms observed : — 
a: oob: CO c; co a: oo b : c; a: b looc; oo a: b: c. 
According to Levy : — 
MM= 90° 10'; 
Forms observ^ed: — 
Combinations observed : — 
MP = 92° 13 ; b:h-l: 0-7027. 
N, P, M, e’. 
110, 011 (Fig. 70). 
110, oil, 001 (Fig. 71). 
110, oil, 001, 100 (Figs. 72, 73). 
The crystals are hemihedral : the faces 0 01 and 10 0 have their parallels, but of 
the four faces of the forms 110 and 011 only two were observed with their correspond- 
ing parallels. 
All the crystals examined exhibit the faces 110, 110, and the faces 011, Oil 
(Figs. 70, 71, and 73). In a single crystal (Fig. 72) the faces ll 0, 1 I 0 , and the faces 
Oil, oil were obseiwed. It is evident that the crystals Figs. 72 and 73 are symme- 
trical but not superposable. 
The crystals frequently exhibit the habitus of triangular tables (Figs. 72 and 73); 
sometimes they are tetrahedrons (Fig. 70), or beveled tetrahedrons (Fig. 71). 
The faces are very brilliant but very often rounded, so that they are apt to yield many 
images and a great ditference in the angles. 
The observed angles given in the above table are the mean of the results obtained 
in the measurement of six crystals. 
Another difficulty in the determination of these crystals is the minute difference of the 
angles of the zones [0 0 1] and [1 0 0]. The results of observation are 1 1 0, 1 1 0 = 90° 10' ; 
oil, 01 1 = 90° 29' ; but I cannot affirm that the second angle is greater than the first. 
For distinguishing the two zones I had at my disposal only one criterion, which is of 
MDCCCLX. 3 Y 
