Vol.. 8, 1922 
PHYSICS: P. W. BRIDGMAN 
361 
from the shift of the spectral Hnes, for if the face of the crystal were ground 
at the proper angle to the reflecting planes, the shift would be increased 
enough to make accurate determinations possible. 
1 Experiment elle Untersuchungen der Rontgenspeklra, Lund 1919. 
2 J. Amer. Opt. Soc, May 1922. 
3 Physic Rev., Ithaca, July 1922. 
THE COMPRESSIBILITY OF METALS AT HIGH PRESSURES 
By p. W. Bridgman 
Je;fferson Physicaiv Laboratory, Harvard University 
Communicated October 17, 1922 
This note briefly summarizes results which will be found in full detail in 
a forthcoming number of the Proceedings of the American Academy of 
Arts and Sciences. A considerable part of the expenses of the experiment 
was defrayed by a generous appropriation from the Rumford Fund of 
the American Academy. 
A new method has been devised by which the difference of the linear 
compressibility of a solid in the form of a rod or wire and the linear com- 
pressibility of iron may be measured with an accuracy high enough to 
give the variation of compressibility with pressure or temperature. In 
addition, I have improved the method which I previously used^ for the 
measurement of the absolute linear compressibility of iron, so that I have 
now measured the change of linear compressibility with pressure with some 
accuracy, and I have also obtained improved values for the change of linear 
compressibility with temperature. By combining these absolute measure- 
ments on iron with the measurements of the difference of compressibility 
the absolute linear compressibility of a number of metals has been obtained. 
If the metal is equally compressible in all directions, the absolute 
volume compressibility may be calculated from the linear compressi- 
bility. The great majority of metals crystallize in the cubic system or 
in the hexagonal close packed arrangement of spheres, and for these the 
compressibility is equal in all directions. Table I gives the compressi- 
bility, X (defined as (dzj/d^)r where v is the volume of the amount of the 
metal that under standard conditions occupies 1 cc.) at atmospheric 
pressure at 30°, the pressure derivative of the compressibility, and the 
change of compressibility per degree rise of temperature for a number of 
such metals. The unit of pressure is the kilogram per square centimeter, 
the pressure range .of the experiments was 12000 kg./cm.^, and measure- 
