1904] 



the Coefficient Volume Elasticity of Metals. 



51 



elasticity (K = K X + K y + K Z ) and e x , e y , e z , the alterations of dimensions 

 caused in the cube by volume expansion in X, Y, Z, 



.. 



In isotropic materials K X = K ?/ = K Z and e x = e y = e zt so that 



* = Pr a /6fc. 



The ease with which minute variations of length can be measured 

 in the case of rods or tubes allows of a very accurate determination of 

 that component of K which refers to stress parallel to the axis of the 

 tube. For this purpose it is merely necessary to so mount a suitable 

 length of tube of the material to be experimented on that it can be 

 subjected to strain by internal fluid pressure, and the variation of 

 length caused by that pressure be observed. 



I have used this method with steel, copper, and brass tubes in order 

 to see whether annealing altered the value of K. The arrangement 

 employed is shown in fig. (1). 



FIG. 1. 



The tube AB is closed by caps at each end. Through the cap at B 

 a small pipe connected with a pressure pump and gauge is introduced. 

 The cap at A has a small hole in it, which can be closed with a plug 

 after the tube has been filled with water. 



The tube is embraced at C and D by gymbal rings fig. (2) where the 

 steel points EE' are closed on the tube, and the pivots FF' rest at 

 (D), fig. (1) on a fixed support, and at C, fig. (1) on a rocking support 

 G. This rocking support carries a small reflecting prism H, whose 

 upper surface is parallel to the axis of 

 the tube, and passes through the axis 

 FF' of the gymbal ring. The move- 

 ment of a mark on this surface of the 

 prism was measured by the microscope 

 M, fig. (2) a ^-inch objective being used. 



The only practical difficulty met with 

 was the variation of temperature of the 

 room during the experiments. From 



this cause it was generally found that the zero was slowly altering, 



E 2 



