170 



BMDGMAN. 



resistance wire B (which is of nichrorne) is mounted in a steel plunger 

 A which is kept pressed by a spring against the upper end of the bar 

 at S. The wire B slides over a contact at C which is attached to the 

 plate D insulated by mica washers at E from the rest of the cylinder. 

 At F the second potential terminal is soldered to the wire B, and at 

 the end G is attached the current terminal. The other terminal is 

 the cylinder itself, to which the lower end of B is grounded. The 

 three wires from C, F, and G are attached at the upper end of the 



Figure 1. The slicing electrical contact device for measuring the absolute 

 linear compressibility of iron. 



cylinder to a three terminal plug, of exactly the same design as used 

 in previous work on electrical resistance under pressure. The plate D 

 is kept rigidly in position by springs shown in section, which are com- 

 pressed as the three terminal plug is screwed into place. There are 

 various mechanical details not shown in the drawing to facilitate the 

 attaching of the connections and the general assembly. The speci- 

 men S is fixed with respect to the cylinder at the lower end. S ends 

 in a disc which is tightly pressed against a shoulder of the cylinder by 

 a spring (which of course must be stiffer than the spring around A) 

 which is compressed by the connections to the pressure producing 

 apparatus at the lower end of the cylinder. 



The resistance between the points C and F was measured on the 

 same potentiometer as was used in previous measurements of the 



