COMPRESSIBILITY OF METALS. 217 



this in three mutual perpendicular directions. This was accomplished 

 as follows. First the casting in its original form, 16 cm. long, was 

 measured in the regular way as a compression specimen. From this 

 casting were then cut four cubes 0.6 cm. on a side, marking the orienta- 

 tion with respect to the original casting, and these cubes were piled on 

 top of each other, and the linear compressibility measured along the 

 axis of the pile for two different ways of piling the cubes together, 

 corresponding to two directions at right angles to the axis of the 

 original casting. These measurements were made in the lever appara- 

 tus for long specimens. The mechanical properties of this casting 

 were quite unusual in that it was very flexible, so that great difficulty 

 was experienced during the machining of the cubes to prevent the 

 casting from bending. The bending was not accompanied by the 

 characteristic noise of the bending of an ordinary casting. It seems 

 not unlikely that the stiffness of the ordinary zinc casting is due to a 

 dovetailing together of crystal grains in different orientations, which 

 cannot be deformed as a single homogeneous mass because of the great 

 difference of the elastic constants of the grains in different directions. 



Dr. G. L. Clark has been so kind as to make an X-ray analysis of 

 this specimen of zinc for me, and finds, within the possible errors of 

 the method, that the crystalline orientation is indeed the same 

 throughout the specimen, and furthermore that the direction of the 

 hexagonal axis is along the axis of the original casting within a few 

 degrees. 



The results found for the cubic compressibility of the unicrystalline 

 casting in three mutually perpendicular directions, (that is, the linear 

 compressibility in these directions multiplied by three) were : along the 

 axis of the original casting 4.98 X 10~ 7 , one of the perpendicular direc- 

 tions, 15.9 X 10 -7 , and the other perpendicular direction 21.4 X 10 -7 . 

 The average of these three is 14.1 X 10 -7 , which is approximately the 

 average cubical compressibility, and would be the result of a single 

 measurement by the method of Richards or A. W. J. The initial value 

 of Richards is 17 X 10- 7 . The initial value of A. W. J. is 17.1 X KH, 

 and their average value to 12000, corrected according to the new values 

 for iron, is 15.1 X 10 -7 . The agreement of this last figure with the 

 average above is as close as could be expected when one considers the 

 possible error of my measurements on four small cubes piled together, 

 and constitutes very strong evidence as to the reality of the large dif- 

 ferences of linear compressibility found above in different directions. 



Tellurium. This material I owe to the kindness of the Raritan 

 Copper Works, from whom I obtained it a number of years ago. I 



