481 
THE VAPJATION OF ANGLES OBSERVED IN CRYSTALS, 
change in the angles made by the vicinal faces with the octahedron face they 
replace :— 
f. 
OOy_ 
o'og. 
o 
15-5 
94 
/ 
12 
15-2 
— 
— 
14 
14-9 
13} 
19 
16 
17 
111 
134 
11 
15-S 
— 
154 
194 
15 
144 
•j 
204 
14-7 
131 
134 
18 
this indicates that, as the temperatnre falls, the vicinal forms become in general 
more acnt.e, their faces make larger angles with each other, hut the angle does not 
depend entirely upon the temperatnre. At 15|-°, for example, 
ojojy is at one time 9A, at another time something between 
15' and 20'. 
The same results were obtained from many other similar 
series of observations. Variations of barometric pressure also 
seemed to be without effect upon the angles of the vicinal faces. 
One suggestive feature was found to he common to many of 
the experiments ; it sometimes ha])|)ens that an octahedron face 
is replaced by two different vicinal forms, one replacing the 
U 2 )per and the other the lower part of the face a„s it stands 
vertically in the solution (tig. 13) ; in such a case it was 
invariably found that the triakis-octahedron on the lower part 
of the face is slightly Hatter than that of the ujjper part. For 
example, a crystal of ammonia-alum, immersed at midnight, t = 18‘9°, l)arometer 
759 mdhms., gave at 1.30 a.vj. the following readings for two appai'ently perfect 
octahedron faces o and w and for tlie cube face A between them. 
350° 1 o', 
A 301° 421', 
247° O'. 
Shortly afterwards w broke up into three images a. /3 y, giving the readings 
a;„3 = 247° 2', 
01, = 240° 46', CO = 246° 56|', coco^ = 0° lOf'. 
VOL. con. —A. 3 Q 
