ELECTRICAL RESISTANCE UNDER PRESSURE. 



135 



The wire was seasoned by a preliminary application of 12000 k^at 

 room temperature, and after soldering to the insulating plug, by four 

 additional applications of 2000 kg. at room temperature. That the 

 seasoning was adequate is shown by the fact that there was no further 

 perceptible change of zero after the first excursion to 12000 and back. 



The readings showed a small but distinct hysteresis, increasing at 

 the higher temperatures. At 0° the width of the loop is 0.45% of the 

 total pressure effect, at 51° 0.5% of the effect, and at 95° 0.67%. At 

 95° there was a displacement of the zero after the run of an amount 

 equal to the width of the hysteresis loop. At the other temperatures 

 there was no perceptible change of zero. 



The results were computed in the usual way, and are shown in 

 Table XVIII, and Figure 12. This alloy is unusual in that the pres- 



TABLE XVIII. 



"Comet" Alloy. 



sure coefficient of resistance becomes less at the higher temperatures, 

 although the resistance itself becomes greater. The beha\'ior is 

 normal in that the pressure coefficient becomes less at the higher 

 pressures at constant temperature. The relation between pressure 

 and resistance becomes more nearly linear at the higher temperatures, 

 which would be unusual for a pure metal. 



"Therlo." This is an alloy much like manganin in its properties, 

 made by the Driver Harris Co. The composition is Cu 85%, Mn 13%, 

 Al 2%. It has been used in the high pressure work at the Geophysical 

 Laboratory as a substitute for manganin in high pressure gauges. 

 The sample on which I made measurements was 0.005 inches in 

 diameter, double silk covered, and wound into a coreless toroid of a 

 resistance at 0° of 127 ohms. This was verv nearlv the resistance of 



