168 BRIDGMAN. 



amorphous cementing material. In a number of cases I have tried, 

 therefore, to justify this assumption. A number of years ago I 

 measured the compressibility of commercial iron in the form of boiler 

 plate along and across the direction of rolling, 4 and could find no 

 difference in the linear compressibility. I have now repeated the 

 same examination for rolled copper, and again could find no difference. 

 Also, in several cases I have measured the compressibility, first in the 

 shape of the unworked casting, and then after the casting had been 

 extruded to a considerably smaller diameter, so that the crystalline 

 grains were much distorted by working, and presumably considerable 

 amorphous material was introdviced. The general result of this work 

 is that no perceptible change of linear compressibility is produced in 

 this way, and it is highly probable that the assumption is correct that 

 the ordinary cast or worked forms of those metals that crystallize in 

 the cubic system have the same compressibility in every direction. 

 The correctness of this assumption may further be checked by a 

 comparison of the results obtained by my method with those obtained 

 by the other methods, which are essentially methods for measuring 

 the cubic compressibility. 



The absolute linear compressibility of iron has been previously 

 measured by me at two different temperatures. 5 I did not succeed in 

 finding any departure of the compressibility from constancy over a 

 pressure range of 10000 kg., but I did find an increase of compressi- 

 bility at the higher temperature. This early work was unsatisfactory 

 to me for two reasons. In the first place the theoretical considerations 

 of Born would suggest that the departure of compressibility from 

 constancy at high pressures should be large enough to measure even 

 for a metal as little compressible as iron, and in the second place I 

 could not help feeling that my temperature coefficient was too high. 

 I therefore have made a fresh experimental attack on this question, 

 greatly improving the experimental method, and have been able to 

 definitely find and measure with some accuracy the change of com- 

 pressibility of iron with pressure, and to show that the temperature 

 coefficient is several times smaller than previously found. 



This experimental work falls into two parts; first the redetermina- 

 tion of the absolute linear compressibility of iron, and second the 

 determination of the relative linear compressibility of iron and 29 

 other solid metals. 





