Vol. 8, 1922 
PHYSICS: P. W. BRIDGMAN 
363 
specimens of the same metal do not yield consistent results, unlike meas- 
urements on different specimens of cubic metals. If a non-cubic metal is 
measured first as a casting and then as an extruded rod, different results 
will nearly always be found. Results on two different castings, even, are 
not the same, unless the method of cooling the castings has been the same, 
so as to ensure the same average orientation of the crystal grains. By 
measuring the linear compressibility of non-cubic metals prepared in differ- 
ent ways, it is possible to set a lower limit to the differences of compressi- 
bility that would be found in different directions in a single crystal. This 
was the method adopted, and in table II are the results for several non- 
cubic metals. The values tabulated are the linear compressibility, k (de- 
fined as (bl/dp)^, where / is a length parallel to one of the sides of a body of 
TABLE II 
SUBSTANCE 
— k AT 30° 
— (-) 
^ k\br ) p 
X 107 
X 105 
X 10* 
Bi 
cast 
7.67 
0.97 
0.9 
extruded 
11.78 
1.82 
3.7 
Sb 
cast 
6.80 
1.39 
1.0 
cast 
4.89 
0.93 
1.7 
Cd 
cast 
4.72 
1.15 
5.6 
cast 
6.51 
1.23 
7.4 
uni-crystalline 
2.86 
0.94 
Sn 
extruded 
6.51 
1.12 
6.6 
cast 
5.67 
0.71 
4.7 
Te 
cast 
—2.36 
Zn 
cast 
1.66 
5.30 
7.13 
metal which under standard conditions is a cube one centimeter on a side) 
at 30° at atmospheric pressure, and its pressure and temperature deriv- 
atives. 
The three measurements on zinc were on pieces cut from the same original 
single crystal, oriented so as to give three directions mutually at right 
angles. For zinc, therefore, these numbers give a fair idea of the difference 
of compressibility in different directions in the same crystal. It is surpris- 
ing that the difference is so large. The mean of the values listed above for 
three perpendicular directions is nearly the same as one-third the average 
cubic compressibility found by other observers, confirming the essential 
correctness of these measurements. 
The negative compressibility of tellurium in a particular direction is 
perhaps unexpected, and so far as I know this is the first case found of 
this kind of behavior, although a somewhat analagous instance, the 
negative Poisson's ratio of pyrites, has been found by Voigt. 
